I Spit In This Beer
A man orders a beer at a bar. Before he drinks it, he has to go
to the bathroom. He doesn't want anyone to drink his beer, so
he puts a note on it that reads "I spit in this beer." When he comes out of the bathroom, he sees something scrawled on the bottom of the note. Under his writing, someone wrote "So did I."

McQuillan
McQuillan walked into a bar and ordered martini after martini,
each time removing the olives and placing them in a jar. When
the jar was filled with olives and all the drinks consumed,
the Irishman started to leave. Excuse me," said a customer, who was puzzled over what McQuillan had done. "What was that all about?" "Nothing," said the Irishman, "my wife just sent me out for a jar of olives."