I play dumb in situations as an assertive technique. It works well when someone is trying to guilt trip and/or manipulate me.
Example:

Inlaw: I need you need to take my cousin to the airport at 4:00am because I can't.

Me: I don't understand, why do I need to do it?

Inlaw: well I can't so YOU have to.

Me: I still don't understand, why do I have to do it?

Inlaw (raises voice getting irritated): well what kind of person won't help their own sister in law???

Me: I don't know....what kind of person would do that?

Inlaw: well fine I'll get someone else to do it!! (Hangs up phone)

It's a great teqnique I learned from a book I read called "when I say no I feel guilty."