Whether we laugh or not is not really the issue - what we "take in" (eyes, ears, mind) on a regular basis is the issue.
If someone tells the right kind of "dirty joke" (that is not instantly too objectionable), I may in fact laugh because it struck me as being funny. A laugh in that case is merely a reaction - because it was actually funny. It is simply the honest truth. That in of itself is not necessarily a sin or a problem.
What is important is a matter of "what we fill ourselves up with" - because, everything that we "take in" can affect the way we think - good or bad.