The black jacket was stitched with "f--- you" in white lettering, repeated vertically down the back, and Oubre turned to show it to a bank of cameras outside as he was arriving at the locker room.
The NBA has a dress code for players on game nights and has the option to issue fines for violations.
Oubre has been fined several times in his career. He was fined $15,000 last week for "aggressively entering an altercation" between teammate Bradley Beal and Golden State Warriors star Draymond Green.
He lost $18,242 last season after he was suspended for Game 4 of the Wizards' playoff series with the Boston Celtics after charging then-C's center Kelly Olynyk. Oubre was fined $25,000 last season for kicking a ball into the crowd. In 2015, he was fined for making an obscene gesture.
The Cavaliers beat the Wizards 130-122 to end a four-game slide.