Dutch truck
n. 1. A mobile store that sells Dutch treats, food items and goodies. Typically operated by a person knowledgeable on Dutch things. 2. informal A person who walks into a private conversation and manages to change the subject of discussion.
ex: When discussing local politics with my friends, John suddenly joined the discussion and asked the participants what people thought of the size of the current Big Macs. Like a true Dutch truck, John single-handedly managed to distract us from the true issues.