Spotted...

Since you ask... I'm sitting on a chair, wheel between legs. Repaired tube is in. I'm running a tyre lever in between rim and tyre to snap it back into place, moving my hand/arm towards me. Lever slips out of rim, hand (holding lever) flies into genitals. Impact = nasty.

Tyre lever to install new tube = fail. The punch in the balls is your punishment.