not to mention the hemorrhoids...it can literally be a pain in the a$$. they have out these things called "butt plugs". you put it in there a few hours just before youre about to have anal sex and its supposed to make it easier for the large to get in. lubes also help too like petroleum jellies.
i may be be straight, but anal sex has caused me terrible scarring problems years after receiving it. i now have internal and external hemorrhoids, painful bowel movements, and an anal fissure (a tear in the lining of your rectum and anus). its not worth it and its even more embarrassing to try to explain it to a doctor or a nurse. :-\
And that also applies to heterosexual couples as well. It can cause tears and infections.
The only thing I can tell you is you're looking for trouble! even if he was average size anal sex isn't healthy I'm sure you know that.