If someone in a group says nearly nothing all the time, let others discuss things, just waiting for the perfekt moment to throw in a gag, you can call this behavior humor snipering.
Most of the time followed by a surpised reaction or laughter (not slaughter, that's the difference to real snipering).
Humor snipering is regarded as a high art by some people.
Also known as Gag snipering
A long discussion about a problematic family structure is going on, about what the problems in the family are and why there are so many suicides.
Person 1: As you can see, the communication has never been very good in this family. Suicide is no communication.
Person 2 (nothing said so far): Yes it is, it's non-verbal communication!
(Followed by a lot of breath-ins and gasps, laughter too)
What Person 2 did was "humor snipering"
A sniperbear is a rare species of bear which is indigenous to the Rocky Mountain National Park in Estes Park, Colorado. This bear is equiped with two .338 caliber L115A3 AWM sniper rifles replaced for its arms. This bear is extremely dangerous avoid at all costs. Too make sure you are safe wear red or have a red roof on your house the bear's bullets can't shoot through red.