“Complicit in faking the moon landing/covering up the Flat Earth™” are the obvious ones. “Space cadet” always a classic. These, being the low-hanging fruit, I think will be the ones we’ll see the most going forward, but I’d still like to throw my hat in the ring:

“An astronaut? You mean those guys that get off on flying their little rockets out of the atmosphere so they can breathe bottled air for a week? Like some sort of oxygen cuck?”

(obviously this implies a repubican pundit using the word “atmosphere” in a complete sentence, so I think we’re safe)