Also heard this one from my old man many years ago:

You wake up in a room with two guards in front of two doors. One door = death, the other = freedom and life. One guard can only lie, the other only tells the truth. The guards know which doors they stand in front of. You only have one question to ask either of the guards to help you figure out which door to go through. What is the question you ask to ensure you choose the non death door?

ask which door would the other guard say leads to freedom. Then take the other door. if you ask the truthful guard he will say the lying guard will point to the death door. If you ask the lying guard he will lie and say the truthful guard would point to the death door. In either case both guards will point to the death door.

I think it would be more interesting to modify this question such that “there are two hot and scantily clad young co-eds”. One is 18 and the other one is 17 and 1/2. Furthermore, you know that one always lies and the other always tells the truth.