It sort of makes sense to me. If I were to kiss someone, I wouldn't want any evidence that those lips had been wrapped around a penis. It can have happened, I just wouldn't want the evidence. So if I was also a guy, then had they given me a blowjob, I would always have that evidence.
Needless to say, girly parts don't bother me. As for my own? I guess I'll find out one day.