AusWang, first, understand that what I'm talking about is consensual play only. If some random person in a locker room or shower said something derogatory about my dick, I'd be as insulted and pissed off as anyone.
But if I'm involved in dom/sub play with someone, then the dynamic might go in different directions. I might want to be dominated physically (say tied up, or slapped around, or just fucked extra hard up and down the walls), or I might want to be dominated psychologically (told I'm whore, or a fag, or a small-dicked looser). In that case, that humiliation just adds to my psychological domination and gets me hotter. Obviously this doesn't work for most guys, but if you search for SPH or small penis humiliation on this site, you'll find tons of men who really get off in it. For folks who enjoy it, that particular humiliation touches something really deep in our sexual desire. You could also look at LPSG groups that include SPH or small penis in their names. SPH is also part of some people's cuckold play, so check those groups as well.
Cheers!