I had an ex who was very un-kinky in general, the only more "unusual" thing he was into, was anal sex. Being in general a nice sweet girlfriend, I said we could try it. Super huge mistake. He was fairly well endowed (7x5.5 if I'm going to hazard a random guess) and he didn't. use. lube. He used saliva and only really worked two fingers in. He then proceeded to try and shove the whole damn thing in, which needless to say caused me to make a horrible sound I hope I never make again, and scrambling away from him out of the bed. Somehow I was stupid enough to allow him to attempt again at a later date, but both times he hurt me and made me bleed. For years if anybody even mentioned going near my ass they got a hell of a talking to.
It's actually only in the last several months that I've had my own burgeoning curiosity about anal play. Someone purchased me a butt plug kitty tail as a gift, and it was on the small side. Maybe 4x4. I had been exploring cautiously on my own, after obtaining an item to give myself enemas, and fingering. I've worked up to another butt plug since, as well as trying other toys. I've yet to experience an orgasm from purely anal stimuli, but I've felt like I was close. Just have to spend a decent amount of time getting used to it. If you're curious about it, I highly recommend exploring on your own, before allowing a partner to try anything. That way you don't have any unpleasant surprises. And hopefully you get something to clean yourself out with, because that reduces a lot of the stress about it, at least on my part. I (eagerly?) await the day I get to try anal sex again with a person, and not a sex toy.