Farting in an elevator 

When you comment on a facebook or reddit thread (usually of political discourse) with a vicious and worthless comment that is only meant to make the rest of the commenters angry for the sake of being a dick. You just say your comment and leave, with no intention of engaging in the conversation.

Like farting in an elevator of strangers as you walk off at your floor, leaving them to deal with your ugly stench.

i.e. When a Hillary person randomly goes on a Bernie person's facebook page thoughtfully discussing healthcare news and leaves a comment like, "You are all a bunch of socialists and you're the reason we have Trump!", or a conservative just goes on a liberals' page and calls them all a bunch of "libtards" and neither respond to questions or comments, that's like farting in an elevator.

I promote thoughtful political discourse on this thread with articulate responses. No farting in this elevator.

The Reddit subgroup "ChangeMyView" has the best rules for keeping people from farting in an elevator.

Farting in an elevator by BruceLeah July 27, 2017