What's a clever way to be funny when someone thinks you're too serious?

Make jokes at their expense while holding a straight face. Lots of eye contact is key

A termite walks into a saloon and asks, is the bar tender here?

Knock knock

Stick 2 baby carrots up your nose...point your chin towards them making donkey braying noises.

Start arguing with the conscience midget on your shoulder..😷

Pull their bottom lip over their head. Then chop em in the throat.
Or....

"Pull my finger" is always a good escape route.

‘Do you want to know how I got these scars?’

A dry wit.

Self deprecating humor

Sarcasm.