What is your favourite opening trap?

Here is a trap in the London System. It doesn't happen that often, but I had it on the board a couple of times.
lichess.org/study/EBzUyAbY/mGNhVNCD

1. d4 Nf6 2. Bf4 c6 3. e3 g5!! And from now some of my blitz/bullet opponents are premoving Nf3, when I play gxf4, or they are going with Bxg5 and loose their piece after Qa5+ and Qxg5 next. I guarantee that this trap works in 90%, I saw even masters falling to this trick.

I was able to play this trap in a blitz tournament of my chess club. It is one of the longest traps I've ever seen.
lichess.org/study/EBzUyAbY/lMmVwsLO

@IAmMateCheckMate I love this trap. All those London System players premove their memorized setup all day long. In almost every game they play the same moves over and over again.
Here is another one, which punishes premoving:
lichess.org/study/EBzUyAbY/Kh7Rmaaw

Other trick that works pretty much always is 1. e4 e5 2. Bc4 Bc5 3. d4?! exd4 4. Bxf7! Kxf7 5. Qh5-Qxc5 with very good play for white. Funny thing about that is this works even in OTB chess, had this position like 5-6 times and 100% of my opponents falls for this. Instead of 3... exd4 black should go with Bxd4! where white gambits the pawn for the initiative.

@IAmMateCheckMate I play the bishop's opening myself. It is a really nice trick. Bxd4 is the critical move.
Here is an article about this move. It's quite unexplored I think and the positions are really nice.

http://www.kenilworthchessclub.org/games/java/2009/movsesian-adams.htm

The london system trap

@Scastangia Wow thanks a lot. I will try this. Even if white plays Nf3 it isn't the end of the world. Black can just play e6 followed by Bd6.

no problem, I actually discovered this from Eric Rosen