Think it was Minecraft, but it may have been GTA or G-Mod.
Iirc, someone asks someone else a question (Gavin asking Jeremy, so says my gut), and there's a legitimate 3-5 seconds of complete silence that shatters the previous conversation with everyone's befuddled amazement. Gavin responds with "I think that was genuinely the longest period of silence that's ever happened in this office."
Oooh see now I feel like a real Caboose lmao. Thanks for the help!
AH Let's Play - "Longest silence in the history of Achievement Hunter."
TipOfMyRooster