I'm sure this applies to smoking as well, but it seems more noticeable with vapes. I think it's caused by not flushing or not balancing nutrient levels, but idk for sure. But you can tell bad cough weed apart from good weed on the very first toke. It will almost cause your lungs to itch and throb, like there was eczema on your throat and lungs. The tingly sensation in the lungs and throat lingers for up to 1-2 hours, gradually wearing off. Normal weed certainly makes me cough, but it never irritates my lungs this much. It's a wetter cough, whereas bad weed gives a dry cough. Maybe not the best description, but lmk if you've had similar experiences.