How would you say if someone invited me something to do sort of things.
example: Hey buddy wanna play video games?
(can i reply) Yes that would be fun, by the way what gives you the idea?.
-Please correct my grammar. Thanks everyone.

Question

Answer

I'd definitely recomend talking more casually. You hardly ever say "yes" to someone your own age, hardly ever to adults, even.
Yeah, that sounds fun.
Asking why they thought of it is...rude sounding, but anyway, the phrase is: by the WAY, what gives you the idea? although you'd probably say, what GAVE you the idea?

Answer

Anushka is right although I recommend that you say, Yeah, that's a great idea, which ones do you like? not what gave you that idea?