Comedy club etiquette and what happens if you heckle
The basics
Arrive before the start so you are seated when the first act walks on. Turn your phone to silent and keep the screen away from the stage, because a lit screen in a dark room is easy for a performer to spot.
Do not film or record unless the venue or the comedian has said that it is allowed. Many comedians test new material and would rather it did not end up online.
Talking during the show
Laughing is the point, and a loud laugh helps the whole room. Conversations are different, because a table chatting through a set makes it hard for the performer and for the people around you to hear.
If you need to leave for the toilet or the bar, go between acts where you can, and keep your head down if you have to move during a set.
Heckling
A heckle is a shout aimed at the performer. Most comedians have heard every kind and have a reply ready, and the audience tends to side with the person on stage, so the heckler usually comes off worse.
If a comedian speaks to you, answering briefly and good-humouredly is all that is needed. Nobody expects a performance back, and a short honest answer is what the comedian is looking for.