Not 21 yet, but my 18th was fun. Went to a restaurant with a bunch of mates, had a very nice meal, went back to mine and drank copious amounts of alcohol (they kicked us out the pub, the gits). Went to bed at 5, woke up at 9, then at 3 went over to another mates house for another party, drank copious amounts of alcohol, then went for a walk at 1:30am getting back at 4am in an effort to find food with a couple other guys. Then kepy myself up until 8pm that night so my sleeping didn't get disturbed too much.
Also found out what the effect of drinking 2 litres of red bull in about 3 minutes does to you