Jabroni
Jabroni is an insulting slang term. In the television series, It's Always Sunny in Philadelphia, jabroni is a word that Mac uses as a mild insult, sometimes in a friendly manner. They think it is a very impressive word and sounds awesome.
The origin of the word jabroni is poorly understood. It has been theorized as Italian-American slang for a stupid, foolish, contemptible person. It has also commonly been used in professional wrestling as a play on the word ‘jobber’ (Wrestlers whose role is to lose to opponents so the opponent can build their reputation). It is often confused for or conflated with the word jiboney which the OED plays up jiboney (in numerous spellings) as a more antiquated version of jabroni. Jiboney is a colloquial Italian-American word that is of uncertain origin and was used mostly on recent immigrants, to create their primary definition of jabroni. The OED’s first five usages are of this jiboney word. First used by the Iron Sheik and made famous by Dwayne ‘The Rock’ Johnson, a jabroni in wrestling is a loser in both the sport and as a person. It is highly likely that the Iron Sheik knew jiboney, heard one of its variances such as jibone or jadroney in usage when he immigrated to the U.S., and that he made up a new version suitable for wrestling.
In Season 6, Episode 4 of It’s Always Sunny in Philadelphia "Mac’s Big Break," Mac starts using the word jabroni while practicing hockey for a slap shot contest at Philadelphia Flyers game. Both Charlie and the local radio DJs that are sponsoring the contest remark on use of the word.