It's Always Sunny In Philadelphia: 10 Most Offensive Episodes

Season 3, Episode 9

Best Quote: Mac: "It's a song Charlie wrote. It's called Nightman. Skip all the raping parts and get on the stage."

Sweet Dee starts to date someone who Dennis tells her has special needs and as the episode continues, Dee starts to believe him.

The representation of a "retarded" person, as the gang so sensitively phrases it, and Dee's lack of a moral compass makes this one of the most offensive episodes of It's Always Sunny. 

There is never a second thought about the right language to use when addressing the situation or as to whether or not judging someone on a mental illness that affects their day to day life is a bit morally ambiguous. The gang plough ahead investigating Dee's new partner as if what they're doing is perfectly reasonable, only for Dennis to reveal that he was lying the whole time to upset Dee, again with absolutely no signs of remorse.

This kind of behaviour and political incorrectness is what fans have come to know and love about It's Always Sunny, but most people may not be so forgiving.