1) When one consumes too much alcohol and becomes angry and/or grumpy as they continue to drink.
Origin: A term coined by DB when discussing angry drunks
The woo-hoo girl drank so much at the bar, she became a grrunk and started some fights.
The bonehead at the party got grrunk after doing 6 kegstands in a row and started calling everyone names.
The piss loaded jock at the bar didn't pick up, so he became a grrunk and started some fights.