a real bitch - A real bitch is someone who calls you out when you're being

A real bitch is someone who calls you out when you're being a total mess, even if it's in public.

You said, 'I'm the best.' She said, 'You're the worst. Everyone knows it.'

You talked trash about her in front of the whole class. She just walked up to you and said, 'You're a total loser.'

You called her a 'total joke.' She said, 'You're the joke.'