You are over 21

A guy walked into a little corner store with a shot gun and demanded
all the cash from the cash drawer. After the cashier put the cash in
a bag, the robber saw a bottle of scotch that he wanted behind the
counter on the shelf.
He told the cashier to put it in the bag as well, but he refused
and said "Because I don't believe you are over 21."

The robber said he was, but the clerk still refused to give it to
him because he didn't believe him. At this point the robber took
his drivers license out of his wallet and gave it to the clerk.

The clerk looked it over, and agreed that the man was in fact over
21 and he put the scotch in the bag.The robber then ran from the
store with his loot. The cashier promptly called the police and
gave the name and address of the robber that he got off the license.
They arrested the robber two hours later.