Maybe the Gibbins Weidenhagen Gambit?
It's at least fun to say
This might not be long, but if you play this regularly your tongue will want to strangle itself.
Delayed Exchange Ruy Lopez Deferred.
Slav Defense: Modern, Alapin Variation, Czech, Krause, Wiesbaden, Sharp Line, 8...Bxe4 9.fxe4 Nxe4 10.Bd2 Qxd4 11.Nxe4 Qxe4+ 12.Qe2 Bxd2+ 13.Kxd2 Qd5+ 14.Kc2 Na6 15.Nxc4 O-O
Nimzowitsch Defense: Scandinavian Variation. Bogoljubow Variation Heinola-Deppe Gambit
1.e4 Nc6 2.d4 d5 3.Nc3 e5
This is the longest i have heard of giuoco piano game: giuoco pianissimo, italian four knights canal variation