Whoever is being penetrated is one of those people who always finds anal sex painful and difficult and thus not very arousing.

They still have anal sex anyway because the comfort and cuddling is very enjoyable and the penetrating partner always rewards them with prostrate massage and milking afterwards etc.

But during sex, it's snarky, sassy, snappy retorts exchanged between them.
Also bonus for
"Just relax! You're crushing my dick!"
"I'm trying!!! You need a smaller dick!"