Psywave lack of super-effectiveness to be fair is something I don't expect everyone to know, but Skarmory's weakness to Electric? It's a freaking Flying type. You know like the Pidgey's you would destroy with Pikachu's Thundershock in Pokemon Red. When people claim to have played since the first games but don't know basic Type knowledge it really surprises me.
It's not the flyingn type that throws me off about Skarmory, it's the steel type that gets me. Steel is the one type I rarely encounter in the game, and the only things I can immediately remember about steel are ground and fighting tears it limb from limb, and it has the most resistance to types. Immediately, my thought process is "electric is resisted, right? I go elec' and this might take a while, go with powerhouse or fire"
Like I said, lot of info, and info that normally doesn't apply to me isn't solidly memorized.
Several series on, and Ash still gets confused by type differences.
In a battle against a ground type
Friend at the sideline "ASH, (insert opponent pokemon name) is a ground type pokemon, electric attacks won't work"
Ash "Rrrrrr, that's right, I forgot"
Gym Leager/Opponent "Ha, I expected better from you Ash"