Suit Up! is a phrase regularly spoken by Barney Stinson. It refers to his policy of wearing a suit for almost every occasion. The origin of the phrase and Barney's suiting up is explained in Game Night. After his break up with Shannon, Barney found a suit store flyer bearing the slogan "Suit Up!" Feeling depressed, he took the flyer's advice (and the advice given to him earlier by the man who stole Shannon from him) and suited up for the first time, creating the Barney we know today. In Single Stamina, Barney explains why he and his brother James suit up; "to distinguish ourselves from the millions of T-shirt and jeans lemmings out there". In Girls Versus Suits, Barney performs a musical number detailing his love for suits and suiting up (the lyrics to which can be found here).
Barney mentions Suiting Up on many occasions, and is frequently frustrated by Ted's reluctance to ever Suit Up with him (although, on rare occasions, such as the Pilot and Moving Day, Ted does Suit Up at Barney's request).
The Sexless Innkeeper: Barney only suits up half, wearing sweatpants (Armani) after Lily and Marshall "dumped" him and Robin.
The Playbook: Barney had to adorn a variety of non-suit costumes to trick women into sleeping with him.
Girls Versus Suits: Barney didn't wear a suit to get with the hot new Bartender.
Doppelgangers: Disguised as a cab driver and a street performer, Barney did not wear a suit.
Lucky Penny: Barney runs NY Marathon in a tracksuit. This is open to interpretation, as to whether a tracksuit counts as a suit.
The Yips: Barney suits down after learning that his first time with Rhonda was a lie.
Stuff: Barney does not suit up when he does his one-man-show.
Murtaugh: At the rave and when TP-ing the laser-tag battle field, Barney is wearing neon hipster clothes. He then pays Ted $30 (apparently double) for his finest suit.
Special Suits
Flight Suit
Barney "flight suit[s] up" for Halloween in Slutty Pumpkin.
