Pluggers and One Big Happy: What's an outhouse? What's a couch-potato? What's a mother-in-law?

I really don't understand how a professional cartoonist could possibly have the gall to use a mother-in-law joke. It's the single most hackish joke in existence. So, of course, seeing it in Pluggers is not even remotely surprising.

The One Big Happy strip below is actually a send-up of mother-in-law jokes. So it's okay.