For me it is the move Neg5 (or Neg4 if I am black). As mentioned here if I get to play this move, it is almost always because I have the big kingside attack going. And it also means I have not one, but two knights involved in the party.
Having spent a lot of the summer player bullet/blitz/10s chess with my son (and losing 75% of the time), he seems partial to g4/g5, especially early in the game. Although he has a far better positional understanding of the game than me, when g4 hits the board, it usually means he wishes to hack me off the board ("bringing the heat" he calls it). It does turn up in both the Keres Attack against the Sicilian, and the Shabalov-Shirov Gambit against the Semi-Slav, so it is a reasonably sound strategy.
To add to his collection of early g4/g5 openings, he can look at the following game from Tata Steel. Carlsen (as black) plays 10 ... g5 against Eljanov, although this is to drive the Bishop back. Eljanov actually gets in g4 a few moves later to stop any kingside shenanigans, but goes a bit to far with a speculative piece sacrifice. Although it gets him a lot of pawns, Carlsen regroups, cleans up the pawn mass, and happily reaches a winning ending.
Eljanov,Pavel (2760) - Carlsen,Magnus (2844) [E10]
78th Tata Steel GpA Wijk aan Zee NED (7.1), 23.01.2016