7
I do and have done so since puberty. To me, masturbating is never as enjoyable if I don't rub the nipples. My technique is to use the longest finger on my left hand to lightly caress the right nipple and the forearm to brush against the left nipple at the same time. I do find though that once I'm starting to get nearer to orgasm, the nipples become more of a distraction than an aid, so I then just stimulate my dick alone.
I can imagine that more gay men might do this than straight men because straight men might consider it to be too feminine to rub their nipples. I happen to be straight but I have boyish good looks rather than a particularly manly face, so my brain might be slightly less masculine than the average male also.
yes usually...