A: You don't you see if you've got 3 condoms.
A: Practice.
Their balls will show.
3, duh. (My ex's 9 year old little sister told me this joke, and followed is up with: "and YOU'RE the math guy!" >< Burned.)
3 blind mice.
A. Every time they were given a corner, they built a shop."
Reality *cries in the corner*
A mental block.
A: It matches their mustaches.