The story
From mald + -ing, itself a blend of mad + bald. First cited usage of "mald" points back to November 2011 with an entry made on Urban Dictionary by user Yozaru. Became part of gaming culture in 2019 through the streamer Forsen, specifically referring to someone becoming so mad at a game they turn bald, either through stress or hair pulling.
Etymology from Wiktionary, CC BY-SA 4.0.