I don't like being touched on the clitoris. I don't like being spanked hard. I don't like being blindfolded. And my attitudes toward anal play and heavy bondage are guarded and tentative. (Hole-y is really just a vagina slut.)
I've always been a bit ashamed of these liabilities, feeling that along with my limited pain tolerance and tendency to fatigue, they make me a suboptimal fuck. A real sex kitten would like everything, right? No holes barred. And if she doesn't precisely like an act, she should at least be "good, giving, and game" enough to do it anyway. (I like a lot of what Dan Savage writes, but "GGG" annoys the piss out of me with its new-age-frat-boy "if you were really sex-positive you wouldn't have all these pesky limits!" logic.") So I've tried, on some unfortunate occasions, to downplay my limits and do it all anyway.
The result was some really shitty sex. My partners weren't idiots or rapists; when I was doing something I didn't like they picked up on it and they didn't enjoy it. When you get down to it, not many guys want to touch a girl's clit just because it's there; they want to touch it to give her pleasure and experience her reaction. So letting a guy touch my clit because I didn't want to be difficult, then gritting my teeth at the discomfort, wasn't really doing either of us any favors.
Food analogy time: telling someone you'd like to have "sex" is about as helpful as asking them to cook you "food." And then getting angry--or worse, choking it down in visible misery--when they serve you a steak and you're a vegetarian. No, a vegetarian isn't the optimal trouble-free diner, but you could have had a delicious tofusteak or whatever the hell vegetarians eat if you'd gone ahead and presented your "trouble" upfront.
Sharing your limits may feel like a buzzkill, but not sharing your limits is a recipe for disaster. Limits can actually make for great sex--this may sound like low standards, but just knowing that a guy won't do anything I dislike is a surprisingly good and powerful feeling. It's all dessert and no veggies. Sex without doing X really means that you'll be doing Y and Z all night, and OH FUCK are Y and Z so fucking good.
(Note: I can't count the number of times I've had the following conversation with a guy:
"So, what are your limits? Anything I should steer clear of?"
"Nope, I'm not real complicated, I just like everything."
"So can I put my finger in your ass?"