(adj) means annoying in a particularly vulgar and cheeky way. To be rude, insulting, and offensive. It is often used to refer to something intentionally oversized or intentionally offensively loud. Bragging is considered obnoxious, as is intentionally disregarding a rule. Showing off your disregard for a rule or order. Being blatantly disrespectful of social norms and those who would enforce them.
I tried to tell nim to turn down his music so i could sleep and that obnoxious asshole stared me in the face while he turned it up, i almost killed him.