Man, I keep looking through my google referral logs and cum swallowing is by far the number one query. Or specifically, distaste for cum swallowing. The most heartbreaking search string was "how to not really swallow cum." Damn... my only suggestions are close-up magic or honest communication with your partner. And that's just when I'm trying to be sensitive. My real knee-jerk reaction is "Why on Earth wouldn't you?"
But I think I'm doomed to never understand this, because I'm just not very squeamish. Confession: if a partner ever wanted me to drink his piss, I would. It wouldn't even be that much of a humiliation thing; it would just be a liquid. (I don't think I'd eat shit, though. Partly for health concerns, partly because I'm a little squeamish. As for merely getting shit on... well, it's not hot to me but if it was really important to him and he could convince me it wasn't a hateful act... mayyybe.)
It helps in sex, I think, to not think that the human body is disgusting. Well, of course, most sane people don't, not overall, but I have heard a lot of people call genitals and anuses disgusting. I joke sometimes that "boy parts are icky," but honestly I think cocks and balls are beautiful. Not just beautiful for what they do to me, but... nice to look at, nice to touch. I don't close my eyes when I put my mouth on a man's cock, don't pretend it's something else. When I say "I love the cock," I don't mean "I love boys" or "I love sex" (although both are true)--I mean I love the actual physical cock.
And the pussy. And the tits. And the asshole. And the entire human body, inside and out, wet and sticky and salty as it may be, is beautiful. A pussy is not an unpleasant thing that must be endured to pleasure a woman--a pussy is fucking awesome.
I don't want to sound like I think I'm the only person on earth who believes these things. I'm sure this is no revelation to most people. But it seems like we have these cultural in-jokes that girls think cock is ugly, boys think pussy is icky, everyone thinks asshole is icky. And that's so messed up.