You're just like your mother.
This line is commonly stated by exacerbated and frustrated parents when their child is misbehaving in a way that reminds them of their partner. But here, the line takes on an additional odd/humorous meaning because these are centaurs and reverse-centaurs. The ambiguity of the genetics, the other parent, what the bad behavior is, etc. contributes to the joke being funny, because it's still a topical/appropriate comment for this hereditarily-confused centaur world.