Because there used to be 2 of them, but it's offensive to joke about that now.
You lift their kilts, and whichever one of them has a Quarter Pounder is a McDonald!
Because somebody divided 14 into 2 and he was the prime suspect
Well, chiropodists like jokes. But opticians like them .
A root bear! (I came up with this joke a few minutes ago. I hope it's funny)