If a comedian tells a joke that you find funny, you laugh. If he tells a joke you do not find funny, dont laugh. Or you could possibly go as far as groaning or rolling your eyes. Then you wait for his next joke; if thats funny, then you laugh. If its not, you dont laugh - or at very worst, you can leave quietly.
If you're a lead actor, people are just waiting to say 'you're too old' or 'you're too unhip.' If you're a supporting actor, you can just work forever.
