Strange man, please don't have sex in my basement again.
I don't ask for much, I keep to myself, I just want some clean clothes to wear, and to do that, I must go into the basement. The next time you and your lady friend visit your sister, do the polite thing and keep all sexual desires to yourself, or at least keep them in the guest room.
Don't you realize I could've been one of your five nieces or nephews coming down the stairs? Come on, our encounter was plenty akward, but that would have been much, much worse.
Think of the kids friend, and don't have sex in the basement.
Plus, to be honest, the basement is just really gross. It has a grotty cement floor and no ceiling. Dude, it's straight out of Blair Witch. Doesn't your lady deserve something a bit more romantic? I suppose not since she seems to favor rather unorthodox sexual postitions.
And one more thing, please don't continue to apologize whenever I run into you outside. I would really just prefer to forget about the whole incident. I am moving at the end of the month (partly due to your antics), so for the next two weeks try real hard to refrain from having sex in my basement or apologizing yet again for the aforementioned incident.
Oh and if you must do it, try not to have sex on the couch that I am storing down there. I really didn't appreciate that either.