Once at a table in vegas.
Him: "Ha, I got your set beat with a straight!" as he slams his cards down on the table
Me: "Last I knew, you needed 5 cards to make a straight" as we all see he's a card short of one...
He not only lost the hand, he just quietly got up and left the table after we all had a good laugh.
Not quite what you were looking for, but I'll always laugh remembering it at least!