Pittsburgh Public Safety -- Proud of Stanley Cup Celebration ... Just Couch Fires & Horse Harassment

Pittsburgh officials are hailing its citizens for celebrating the Stanley Cup "responsibly" Sunday night ... except for the one moron who was arrested for harassing a police horse.

The Pittsburgh Public Safety Dept. says ... for the most part, people celebrated responsibly -- no riots, no pepper spray, no major incident whatsoever.

But there was SOME stupidity.

Firefighters were sent to put out 2 couch fires and a mattress fire ... and cops responded to a 20-year-old male who was "taunting a Pennsylvania State Police horse."