What does it take to be funny spontaneously? A good memory and quick thinking – the memory to remember jokes, the quickness to find a fitting joke for the situation before others.
Practiced funnyness also uses acting skills, which are acquired with time and effort. Intelligent people gain skills faster. Confidence always helps – a shy person dare not tell the joke or act in a funny way, because that draws attention. The caveat “if they want to” in the title is due to the possible confidence issue.