Learn! Is your penchant for punning a sign of brain damage?
Know anyone who can't help but make lame jokes and puns? Like, all the time? Maybe they have brain damage.
Okay, sort of. What it means is that compulsive joking (diagnosed in German as Witzelsucht) is an actual thing, where people are constantly coming up with jokes and must share them. People with Witzelsucht find their own jokes hilarious, don't necessarily care much for the jokes of others, and are compelled to share their jokes no matter the situation (like a man waking up his wife in the middle of the night to tell her a joke he had come up with).
So your uncle's bad jokes probably don't mean he's brain damaged, but joking to this level is actually an early indicator of dementia.