The problem with the 'My Mom' Running Gag

So as you know as much as Muscle Man is a likeable character by the later seasons, there's a problem with the running gag that I have and that's the 'My Mom' gag.

Since it's "Who know else [Thing]? My mom! Which is funny the first few times but the longer a running gag goes on, it no longer becomes humorous. Because the thing is no one groaned and finished the sentence of saying 'your mom'

I mean Benson had called him out on it in one episode or the episode of where Moredecai and Rigby to a point where they make fun of his mom and him and his brother force them to eat a piece of paper that turn out to be a butt cheek he made to look like a face.

The real problem with the running gag is that it's the same joke with no variation to it.

Thanks for coming to my TED Talk