Trina bought a Nick Bobblehead from Barney in the episode Six Strings of Evil. She wanted to to be a bobble head that would nod it's head when she tapped the head of it. However, when Barney was putting her bobble head together, Kin and Kon tricked him into getting a head that would shake it's head when it was tapped. Trina asked it a bunch of questions but he shook his head in response to all of them which triggered her into going into Diary Mode.
The Nick Bobblehead is a Bobblehead that looks exactly like Nick Mallory.