During Game 1 of the Eastern Conference Finals, Kevin Garnett and Rajon Rondo were "staring" at each other over a blown defensive assignment. At least according to Doc Rivers. Doc told reporters that it happened early in the first quarter and resulted in him needing to call a timeout to clear the air. The video below shows the only "argument" between KG and Rondo in the entire first quarter (that was on camera, anyway).
The defensive mix-up occurred at the 10:49 mark and a timeout wasn't called until the 5:46 mark, by the Orlando Magic. The Celtics didn't officially call a timeout until the 2:18 mark in the first quarter. Here's the video, you guys can decide.