OK, you know that the ! operator means factorial.
By the basic rules of algebra, 11x/x = 11, because the xes cancel out.
If you're symbol-minded, you might get carried away and claim that 11!/! = 11 by the same rule. The absurdity of this statement is what makes it funny.
If that doesn't make you laugh, than maybe I should fall into an open sewer and die*.
*Mel Brooks reference
"For shame, gentlemen, pack your evidence a little better against another time."
-- John Dryden, "The Vindication of The Duke of Guise" 1684