Surprised Pikachu
Surprised Pikachu is a still of Pikachu with its mouth wide open, used for fake shock at a completely predictable result, usually one you caused yourself. The setup describes a bad decision; the punchline is the face.
Known in the US and across East Asia

What it means
The classic format is a short story: “I stay up until 4 a.m.” / “I’m tired the next day” / Pikachu. The shock is the joke, because nobody should be surprised.
It’s gently self-deprecating when you use it about yourself and a light tease when you use it about someone else’s choices. Either way it reads as playful, not harsh.
Where it comes from
The frame comes from an early episode of the Pokémon anime from the late 1990s. It took off as a meme around 2018, first on Tumblr and then on Twitter and Reddit, and became one of the internet’s standard reaction faces.
How friends from other cultures read it
Pokémon is Japanese and known everywhere, so this is one of the safest memes to send across cultures. Chinese users call it 震惊皮卡丘 (“shocked Pikachu”). In Japan, where Pikachu is a national icon, playing with the format is more of an English-language habit, but the face needs no explanation.
The only trap is irony: someone reading literally may think you really are shocked. A short setup line before the picture makes the joke obvious.
How to reply
Play along: admit the obvious (“who could have guessed”), or answer with another consequence meme, like This is fine. If it’s about your choice, owning it is the funniest reply.
MemeWingman