If you ever meet Mark Lawrenson, mention Robin Friday, and watch his face!
From Wiki, not the most reliable of sources I know, but if he did take a dump in Lawro's kit bag then bravo sir!
"Friday was marked during the game by Mark Lawrenson, who so frustrated the Cardiff forward with his close attention that Friday waited for Lawrenson to attempt a slide tackle and then kicked him in the face. After receiving a red card, Friday left the ground with the game still going on; according to legend, before leaving he broke into the Brighton dressing room and defecated in Lawrenson's kit bag."