I never make a report or call someone in if the person just does it for less than a minute. The civilian glitch is pretty funny to see for a few seconds, and people usually stop after those few seconds. Sometimes you get an idiot who does it for an extended amount of time, but most people just do it for a moment of giggles, then keep on playing.
If you over-react, you're just ruining someone's moment of fun. However, blocking sniper scopes is always a dick move, as are the other actions that are defined as griefing. But a quick Spycrab down the hallway never hurt anyone.