Mine would probably have to be when I beat Liverpool (cpu) on 6* in the Premiership, playing as Arsenal. I was losing 3-0 after about 30 minutes, after Baros had scored a tap-in and a penalty, and Xabi Alonso scored a fantastic curling 30 yard free kick past Almunia. The League was really tight at the top at the time, and for the only ever time, for a split second I thought about turning my Xbox off
Fortunately, I managed to control myself, and ended up beating them 5-4. If my memory serves me right, it was an Henry hat-trick and a Pires brace. I was winning 4-3 in the 85th minute and then bloody Le Tallec, of all people, scored a powerful header. Fortunately, Henry, from the restart then proceeded to sprint past the Liverpool defence and was brought down by one of them, for Pires to dispatch the penalty and claim a 5-4 win, allowing me to stay level with Chelsea and Man U at the top of the table