armchair scientist 

Someone who has no professional training in science yet has the same augmented ego and clout (and on occasion, the same amount of knowledge on the subject).

Your subconscious is actually the excrement of an opalescent Monodon monoceros. I know. I'm an armchair scientist.

armchair scientist by Mesozoical November 22, 2011

Armchair Rocket Scientist 

A person on social media who’s only engineering experience is in stock Kerbal Space Program telling people that a team of hundreds who have years of experience don’t know what they’re doing

A person who doesn’t know what the fuck they’re talking about

CS_Skeptic said that Starship can’t fly because the flaps will tear off. What an armchair rocket scientist!

Armchair Rocket Scientist by TheRealSheep5 January 31, 2023