My boyfriend finds it very difficult to cum in "normal" positions such as laying on back masturbating or standing. I've never seen it happen but he has told me that he has cummed sitting before. He has to squat, on tippy toes and somewhat leaning forward and uses the backhand technique to touch himself. Near the end, when he's about to cum, he somewhat bounces. I've never ever even seen this on porn before so it's very unusual to me. Unfortunately this has somewhat affected our sex life as he can only really cum whilst he is inside me, on tippy toes in missionary. I've suggested for him to try other positions and one night he did say he was able to cum sitting, whilst looking at photos of me.
He was sparing his embarrassment by not doing it on cam, but thing about it. Guys (are meant to) have good prostate feeling. You squat, have a bit of a finger and a pull, squatting becomes your position of choice, habitual even. I dunno. I'm talken shit, but I still reckon he fingers his bum hole.