For me it's the humiliation and exposure. It feeds my submissive side

I think it is not only men that liked to be watched while tossing a load. In a short period of time after my wife Bibi and I were first married in 1968, we went through a short period of expressing our sexual activities with a couple other couples. We both really enjoyed masturbating and would do it in front of each other, do it to each other, and do it with a couple selected other couples. Bibi loved to stroke my cock and have me cum while watching the other couple watch. That almost always led to the other couple picking up the hint, and spilling their load for us to watch.

For me it's allot about the control, and being "forced" to perform in front of someone. I enjoy giving up control over how long I am allowed to masturbate, and when I am allowed to cum.

I don't know why, but it sure makes me cum harder. I used to masturbate in a chat room, and loved it when I had an audience. There was one lady I would masturbate for more privately. One Christmas Eve, she was having a party, and I got to masturbate for all of them. There were several ladies taking turns chatting with me while I was stroking. (just thinking about it now has me jerking off).

A couple of times at a massage, the masseuse watched me stroke until I shot a load. Someday, I want the masseuse to feed me my cum.

not sure why but having someone watch me stroke and cum is insanely hot! I like the feedback and appreciation, I like to watch them finger their pussy or stroke their cocks watching me. Started out only stroking for women, then there was a couple who liked me, and finally started accepting dude's to watch. I still cum twice as hard as anything else I do!

Hard to say why I like to be watched.
It turns me on big time though!
Especially like it if they tell me what to do!

I think it's part of that old "forbidden fruit" thing!

The idea of exposing myself naked and masturbating to another person or persons is really what gets me off. I spent 50 years of my life hiding my passion for masturbation and now I can share it with others. In the process, I've discovered how many older married men are obsessed with masturbation like I am.

Partly because I'm a natural showoff. And when you are really hard and someone is watching, it is an amazing turn on. The cum is super intense.

I get horny just thinking about someone watching me. I love to show off! I really like fucking my fleshlight while people are watching.

Totally agree with buster3333. I just get harder when someone is watching and getting turned on by my cock.

I think it is due to sexual repression. It's one of the most natural things any person does in their lives, but we grow up being told it's dirty, nasty, wrong, sin, etc....so it's something we do in secret and don't tell anyone else until you or a friend finds the courage to bring it up and talk about it and confess to enjoying it, but usually if you bring it up around female friends when you're young or admit to doing it you would likely (in my early days anyway) get the reaction of "eww you're nasty! You're gross! You're a pervert!" or similar reactions because they were taught the same things and girls usually don't open up about it until later on, if they do at all, with most guys unless it is with their friends or their boyfriends, then after a few relationships they loosen up and realize that all guys do it and if they weren't already doing it in secret and being hypocrites about it they eventually start masturbating themselves and as they get older and talking more with other friends about it they become more open with it.
But I think sometimes part of it could be that you get to do something naughty and you have someone being naughty by watching you and maybe the guilt turns into a turn-on, or maybe a bit of nervousness that you are finally able to be open with someone enough to jack off in front of them but should you be doing it and are they going to look at you like a perv after even if they seem okay with it now? Kind of the same thing as people masturbating or having sex in places where the risk of being caught is a turn on to them.
I think there is also that "Oh my God, this is really happening, I have a girl (or guy) watching me jack off" the "Dream come true" kind of feeling that you feel for a while as well. You enjoy the feeling of freedom and excitement.

But after you've done it enough (which "enough" could be a few times for some people while for other people could be many more times and could get the same feeling all over again when you do it with someone new for a while) then you can be more comfortable and there is less of the feeling of it being naughty or taboo, but still a huge turn on just being with someone you are comfortable enough to have watching you especially if they enjoy you watching them masturbate and you can both just feel free to be yourself and do it whenever you feel like and they love sharing in it with you.
I did have one girlfriend once who hated that I masturbated at all, even when she wasn't there, but I was horny all the time and I jacked off a lot, even though we had sex all the time. I could fuck her 3, 4, 5 times back to back and then still want to jack off when I was done, or liked to watch porn and have her watch with me and sometimes we'd fuck and sometimes I would jack off while watching. She just got offended by it thinking I would rather jack off than fuck her, but I fucked her way more than I jacked off, but sometimes I just like to jack off. I never felt guilty about it, although she tried to make me feel that way, and she always said it was nasty, but I thought she'd eventually get used to it or not. Thing is she always stayed there and watched me, even if expressing her displeasure inn some way about it. And oddly enough that too was a huge turn on that she was against it, yet continued to stay there with me and watch me jack off.
I think she was most upset when I jacked off to porn magazines because I was just looking at other girls in the magazines. She was alright with the videos when we fucked as we watched, but not so much when I just jacked off, but I also jacked off a lot when I wasn't looking at any porn and she'd still get upset. I could understand if I was jacking off and looking at other women in porn 50% of the time or more and just ignored her, but she and I fucked constantly and when I masturbated I tried to get her to join me, but she said she would never do that because it was nasty. I had to ask her why she sucks my cock and swallows all my cum (which she would not do for a long time and would not let me go down on her pussy until I finally got past her trying to stop me once and finally got my tongue on her clit long enough that she gave up trying to stop me. lol Then I finally talked her into sucking my cock) I asked her how putting my dick in her mouth and swallowing cum she could do but touching her own body was nasty. She said she didn't like sucking my dick but she knows I like it and it makes me feel good so she does it, but she would never play with herself no matter how much I asked her to. And she never did.
My ex-wife, on the other hand, loved watching me masturbate and loved to masturbate with me. Most girls I have been with loved it or have at least been okay with it, which is great because I have always been turned on by being watched jacking off and watching my girls masturbate, not matter what the reason is that it turns me on.

Yes, when turned on and nicely hard, being watched and encouraged is a very, very big turn on for me

Love flashing women, it's like I feel powerful and manly but also vulnerable at the same time. Such a rush.

I am Rubbing my Throbbing cock Right now to this Hot post and the others.
It's So Liberating to openly masturbate with others.We know how much we Love to pleasure ourselves.We can relate to other horny men and women.
My most Intense Cumm was in a adult theater watching other men exposing their cocks and openly masturbating. It was So Liberating exposing my Throbbing cock and masturbating for them.You could see other older men taking their cocks out and enjoying masturbating in a porn theater.