Me: Can I use the bathroom? Teacher: I don't know, CAN you?  Teachers don't realize that we can of they say he's but we can't if they say no. Because we aren't gonna go in public and we are allowed if it's an emergency. So technically saying "can I use the bathroom" would be grammatically correct?
the may/can line of nitpicking is obsolete anyway. 'can' can mean 'may'