"The Gang Gets Held Hostage" (Season 3, Ep. 4)

In this one, the gang gets a surprise visit by the McPoyle's and the associated mischief that ensues. The gang except Frank are met at the door with their captures.

"Sweet Dee Has a Heart Attack" (Season 4, Ep. 10)

One of the most iconic memes from It's Always Sunny spawned from this episode. In a manic episode, Charlie ends up mapping the mail he was supposed to be sorting all along the walls in the mail room and crazily looks back at Mac.

“The Gang Wrestles for the Troops” (Season 5, Ep. 7)

In a money scheme inspired by Dee's pen pal from the Army, the gang arrange a wrestling match in which Frank, Mac, Dennis, and Charlie are all participated in. The iconic scene linked above is the walk up song for Mac, Dennis, and Charlie as "The Birds of War". This episode is also where Frank's quote from above originated from.

“The Gang Gets Stranded in the Woods” (Season 6, Ep. 11)

While on their way to a charity event in Atlantic City, the gang gets stranded in the woods and their antics ensue. Above is a clip from Mac explaining how he wanted to empress his childhood hero, Chase Utley.

“CharDee MacDennis: The Game of Games” (Season 7, Ep. 7)

Being the first episode centered around the five main characters and them only, they are confined to their boredom within the bar. The game is mainly a derivative from their college drinking antics and the last man standing wins. Frank had never played before and brings an interesting advantage to the table as a contributor on Mac and Charlie's team.

“The Maureen Ponderosa Wedding Massacre” (Season 8, Ep. 3)

Iconic. Just iconic. There is nothing else to say, you just have to go watch it.

“The Gang Saves the Day” (Season 9, Ep.6)

In this episode, the gang stumbles upon a stick-up and it's up to them to 'save the day'. Each member of the gang has a fantasy of what they would do to help, but only one can act.

“The Gang Beats Boggs” (Season 10, Ep. 1)

In this one, the gang attempts to drink 70 beers on their flight, a record set by Wade Boggs. Only two stand at the end of the episode, but you'll have to watch to find out who.

“Mac and Dennis Move to the Suburbs” (Season 11, Ep. 5)

Another endlessly iconic episode which resulted in the meme above. The title kind of speaks for its self.

“The Gang Goes to a Water Park” (Season 12, Ep. 2)

This is one of my favorites from the unique water slide scenes to the bond that Dennis makes with a young girl, showing her "the ropes" of scamming.