Let me think

An excuse that made by someone who is clueless and doesn't want to help, but tries to escape the task given. It is also a word to avoid being asked.

Person 1: Hey, can you help me?
Person 2: Uh, let me think *comes up with a lot of excuse*

Let me think about that and forget it quickly

A phrase you say to someone when you don't want to consider their suggestion seriously.
A phrase you say to someone when they have an egregious suggestion or opinion.

Can I guy your gaming chair for $5?

Let me think about that and forget it quickly.