Hmm.. About the whole penis thing, look here. I basically covered a lot of that in here.. http://www.virtualteen.org/forums/showthread.php?t=9572
Basically, it's being turned on by the act of sex itself. Like, almost thinking of how he could use that on a woman or something.. Not exactly like that, but somewhat.. It's more sub-concious than anything.
It's kind of like how guys have a unwritten respect for other guys with big dicks. Not because they're gay.. They just do.