Is there a word or a term for someone who laughs out of place?

Question

Imagine a person, who laughs for no reason. And then imagine another person, who starts laughing 10 minutes after a joke has been told.
Is there a word or a phrase to describe any of such persons (in non-offensive way)? Maybe, some regional expressions?

Answer 1

«Ridere a scoppio ritardato» when you start laughing way after you should have.

«Aver la riderella», «esser preso dalla riderella» when you can't stop laughing (as mentioned by others above).

Answer 2

Both acts could be be expressed by means of a perfectly legitimate Italian expression: "ridere a sproposito".

Answer 3

For the former case, the proverb says "il riso abbonda sulla bocca degli stolti" (there's a lot of laughter* in the stupid's mouth) For the latter case, what comes to mind is the highly irregular expression "essere tardo di comprendonio" (literally, to be slow of understanding), but neither of these are any pleasant on the receiving end. Euphemisms in informal situations could be commenting on your friend's amount of intoxication or in the latter case likening him to a diesel engine: he's slow but he gets there. In more formal situations it's probably polite not to comment.

If you're approximately in your 20s, really friends and he's been in Italy in the past few years you could even risk quoting Zelig: "oh, ma ci sei? sei connesso?"

*riso means both laughter and rice

Answer 4

As for the first question, there is a quite colloquial (and regional?) word, stupidera, that denotes that kind of laughter when you cannot stop laughing, and everything makes you laugh even more.