mental flashbang

Something so unexpected or outlandish that you shut down for a second. Usually without clarification from the speaker.

Bill: "I was eating these really good chips that I found at Dan's house but I didn't know the name. turns out I was actually eating his cat's shit"
Hank: "..."
Bill: "...so I was at the arcade the other day..."
Hank: "What the fuck dude? you're just gonna drop a mental flashbang like that?"