Here's a fun trick.
The next time you meet someone who suffered head trauma that caused amnesia, tell them you were there for them the whole time they lost their memory.
They'll say, "Hmmm, I don't remember that", and you'll say, "Of course not. The doctor said that would happen."
You can even add in things like, "Can I have my $500 back?", or "When's that trip to Paris you promised?"