On August 17, 2005, Lionel Messi made his debut for Argentina in a friendly against Hungary in Budapest. Just 44 seconds after coming on as a substitute for Lisandro López, the then-18 year old was deemed to have lashed out after having his shirt pulled by a Magyar defender and was sent to the dressing room by well-known whistler Markus Merk.
You can make your own mind up about whether there was real intent behind the collision - the other lad certainly wasn't interested in shrugging it off and went down holding his face despite the fact that Messi's arm seems to make contact with his chest. Either way, the dismissal seems to have a lasting effect on the Argentina - he's never been one to react easily to provocation, and hasn't seen red since.
For the record, Argentina won the game 2-1, with goals from Maxi Rodríguez and Gabriel Heinze. Sándor Torghelle netted for the central Europeans.