What is your reaction when someone is telling a lame joke?

We have all experienced it, that someone tells us a joke but it simply is not funny.
It is lame, it is old, it is childish, it is whatever it is but it just gets no laughs.
How do you react when there is just the two of you and you are the one the joke is directed at?
Or you are in a group of people and one of you tells a joke and it goes deaf on the whole company, and nobody laughs?
How do you react?
You laugh your best fake laugh?
You pretend you didn’t hear the clue?