How to say “you’re banned” in Spanish?
Such as in “You’re banned from the swimming pool!”

Question

Answer

"estar vetado" (formal)
"no puedes/no tienes permitido/tienes prohibido..."

especifically from the swimming pool, i'd say:
"tienes prohibida/o la entrada/el acceso a la piscina"

saludos!

Answer

to ban - no dejar entrar

You're banned from the swimming pool / ya no te dejan entrar a (en) la piscina.

Answer

Estás prohibido de ir la piscina
Tienes prohibido entrar a la piscina
Estás suspendido 
Has sido expulsado de..
No eres aceptado en ...