The person who makes room for laughter has done something useful for the gathering.

Laughter needs somebody to make it permissible. Groups often sit at a careful, slightly stiff pitch until one person says the light thing, and afterwards the whole room talks more freely. It looks like nothing and it is doing structural work, because ease is what lets the real conversation arrive. Whoever provides it is rarely thanked for it.

If a gathering feels tight, offer something small and unserious rather than waiting for the mood to shift. When somebody else does it, laugh instead of leaving them out there alone.