The Big Bang Theory Season 2 Episode 16 : The Cushion Saturation
A paintball game leads to a romance between Howard and Leonard's former girlfriend, Leslie Winkle (Sara Gilbert). At the apartment, Penny accidentally shoots the paintball gun at Sheldon's couch cushion, and she and Leonard have a hard time getting it cleaned. Naturally, Sheldon freaks out when he finds out his favorite spot has been damaged. In the end, Sheldon is still dissatisfied with the dry-cleaned cushion, and he team-kills Penny in the next paintball game, causing the others to "surrender, then (go to) Denny's".