Gattitude is in reference to the Braves catcher Evan Gattis. During the Braves/Nats matchup earlier in the season, Gattis went 2 for 11 with a homerun and 4 RBIs. I guess that is slogan-worthy if you are on the Braves.
The Braves always have problems selling tickets and I guess a little trash talk slogan couldn't hurt (unless the Nats take it personal). Last season the Braves had THOUSANDS of playoff tickets available while in DC the Nats sold out their entire series, so I doubt this will work too well. (The Braves lost the play-in game, so the games weren't played).
The Nats will begin the 3 game series with the Braves on Monday in Atlanta and hopefully the players see this and defend their terrible Natitude slogan. It may be corny, but it is OUR corny.