brąchać 1. „mieć wątpliwości”; 2. „gadać za dużo”; 3. „opowiadać głupstwa But we don't use this word normally

Meaning of that may depend on the context. I think the most common meaning of "nie brąchaj" is "stop saying nonsense" or just "shut up". But it can also mean "don't be mad". It's something similar to colloquial "nie fochaj się". Or "stop complaining". If someone provokes you to a fight, you can say "nie brąchaj się" to tell him to stop, or he'll regret it. Something like "stop messing with me". Activity you use egg beater for is also "brąchać". brąchać jajka - to beat eggs. brąchać ciasto - to mix cake. It is also humorous way to say "to masturbate" or "to have sex", so "stop masturbating" "stop copulating" is also an option :) I'm curious, where did you hear it? It's a made-up verb which is not in dictionary :)