Green’s Dictionary of Slang

(US prison) gossip.

2000		Other Side of the Wall: Prisoner’s Dict. July 🌐 Grapes: Gossip. As in ‘Give me the grapes on her.’.
2005		Prison Slang Mommyblogger mydogharriet.blogspot.com 23 Sept. 🌐 If you press her friend she might give you the grapes on your little jitterbug.