I personally have not heard it used that way. "Pop off" has many meanings and we can only know if you give us the full context.

Pop off: I use this phrasal verb sometimes. When I bake something like muffins or macaroons, I usually grease the pan or the mould before pouring in the batter. With this, the muffins could easily pop by itself when it's done. When a person suddenly gets angry for unknown reason, his anger suddenly pops off. Just like cooking pop corn: It pops off or pops out. Example: Cover the pan when cooking pop corn. When the pan is heated, the pop corn pops out or pops off the pan.

The range of different answers you have had to your question illustrates the nature of colloquial English : it very much depends on the place and people to whom you are speaking. Like Benjamin, I have never heard the expression used in the way you describe, but it may well be so by others. Unless you are confident about the use of ‘slang’ expressions, they are better avoided.

I'll be honest, I have NEVER heard anyone use this phrasal verb to mean the same as "to go something off your chest / out of your system" 'Pop' used as a verb, has been frequently used in the following ways: to go briefly: I'll just pop down to the shops to shoot: they popped off a few rounds at the cans on the fence to materialise an idea: It just popped int to my head! It just popped out of my mouth! to verbalise in quick succession: He popped out a plethora of random facts. If, as has been suggested, the use of this phrasal verb 'pop off' is indeed AAVE with your connotation, I would not be trying to use it or teach it with the intent of daily use. I might raise awareness though. I am surprised by the amount of other tutors here attempting to convince you of the authenticity of this expression and daily vernacular - I can only say that it is not language I have ever encountered in this way.

This phrase originated in AAVE and means largely what you’ve said, but also means “to speak confidently/forcefully about something before knowing all the facts/without knowing much about the situation you’re talking about”