Shirley is remarrying Andre. And Abed and Troy were specifically asked to be normal for the occasion; even if it's just a practice wedding for now.

well, Troy and Abed decided if they spend the whole day in the Dreamatorium, they'll empty their weirdness, and get to be normal at the wedding practice. That's why the two locked themselves in the Dreamatorium since 4 P.M., right after classes, all the way to around 8 P.M., before the wedding practice.

And somehow, it actually worked. They managed to become a lot more.. "normal"; even wearing suits and ties and fancy clothes.

So there they stood, in the Greendale school library, where Britta had managed to set up complete wedding decorations, with Andre standing awkwardly by the priest in his wedding outfit, and Shirley and Pierce nowhere to be seen.

it was even weirder, seeing Abed and Troy be "normal", and sat on a bench, laughing at "non weird" things.