Tommy: "Is there something you forgot to tell me about?"
T.L.: "Nothing comes to mind."
Tommy: "How about a 5-foot-3 blonde with an ass like a breadbasket?"
T.L.: "Oh, yeah. She spent the night."
(from Landman, season 2, episode 10, regarding the character Cheyenne)
Brainbasket is basically where Foxythebloxer (scr33n_p4r45173 on discord)'s brain currently is, in a basket. In other words, another way of saying dumbass.
Foxy: My ai is NOT FURSUIT!
You: bro, you're a brainbasket.