The word comes from a meme image and is used to signal that the speaker knows the position is not the product of analysis. Stonks only go up is the standard joke, deployed in exactly the conditions where that is least true.
The irony is a genuine social lubricant: it lets people post speculative positions without claiming expertise. It also lets them avoid ever stating a thesis that could be wrong, which is how a joke position becomes a real loss.
Related: tendies, yolo, bull-market-genius, degen