Is "Can I go to the washroom?" correct?

Why

Rohit's usage is extremely common in everyday, casual speech, and most people would understand him perfectly and not think twice about it. Traditional grammar, though, keeps "can" and "may" for two separate jobs: "can" describes ABILITY — whether something is physically or practically possible ("I can lift this box") — while "may" describes PERMISSION — whether something is allowed ("May I lift this box?"). Strictly speaking, "Can I go to the washroom?" literally asks whether Rohit is physically capable of going, which of course he is — the actual question he means to ask, whether he's ALLOWED to go, is what "may" is specifically built for. Test: notice the classic teacher's joke response to "Can I go to the washroom?" is "I don't know, CAN you?" — poking fun at exactly this ability-versus-permission mix-up, which only makes sense because the two words genuinely mean different things. His teacher is right: traditionally, "may" is the correct word for asking permission, while "can" is reserved for asking about ability — though "can" for permission is extremely common in casual, everyday speech.