eating lunch alone in a toilet stall
Slang referring to the practice of eating lunch in a toilet cubicle to avoid being seen eating alone, often associated with social anxiety or workplace/school isolation.
He doesn't have any friends, so apparently he eats lunch in the toilet stall.
Compound of 便所 (toilet) and 飯 (meal). The exact origin is uncertain, but it emerged as internet slang describing the social phenomenon of eating alone in a toilet stall.