The joke was new, unforced, and funny then. It actually made sense in context. Now they just retell it every single page out of habit and laziness whether it fits with what's going on or not. It's not like they haven't had time to grow the character, or write some new material. It's been years.
I'm fine with Jim's characters doing silly things being a running gag. I'm not fine with it being the point of the strip every single time he's on screen.
Then again, this is worded a bit strongly. It's not like I'm actually angry about it or anything.