Typos on public notices. Especially Freudian typos, like this one I saw in the craft department at Wal-Mart:
"Costumers please note: there are no refunds on cut fabric."
EDIT: For those of you who missed the typo, I'm pretty sure they actually wanted their customers to note the refund policy. I've noticed this particular typo in other places before, but it struck me as particularly funny when it was used in reference to something an actual costumer might purchase.