Then tell your boyfriend your preference.
If something doesn't feel right: stop! But if the angle is wrong in anal sex, with too much of a sharp upward or downward angle, a sting-y and unpleasant pain can be the result.
Seriously, if Ashley Madison has taught us anything, it's that you can, and invariably will, get busted if you sign up for an account.
Blame it on the alcohol and move on.