Be anyone's slang
Be very likely to accept sexual or amorous advances from anyone.
He had made advances to that girl when she was drunk, but she told him she wasn't anyone's.
I think she will agree to have sex with you after three shandies. She's anyone's!
The origin of this slang is not clear.
To punish someone or something harshly
He's a really strict teacher, so he'll definitely lower the boom on you if you don't do your homework.