In approximate ascending order of geekiness:
-Lots of 3 or 4 a-side football
-Table football
-Skimming stones
-Many video games (definitely my biggest timesink growing up) e.g. Mario Kart, Goldeneye, Smash Bros, Diablo 2
-Common board games e.g. Monopoly, Risk
-Quirkier board games, e.g. 221b Baker Street, Go
-Fantasy booking my little brother's Bionicle collection as a wrestling fed.
-Classic geek games e.g. Warhammer armies game, Magic: The Gathering card game
-A weird story writing duel game my friends and I made up to play during class where we'd invent a character each, and take it turns to write a paragraph of a story of them fighting each other. You won if you wrote a death for the other player's character that they couldn't think of a way to write themselves out of.
-Competetive microrebellion. My friends and I weren't really ones to get in fights (despite my pending showdown here with Neptune), or to bully others or insult teachers, so we needed other ways to express our teenage rebellion. Actually, one friend and I systemised it: we drafted a list of minor misdemeanors to commit in class. Stuff like who could last the longest into the lesson without sitting down, or going and writing on the blackboard unprompted, or playing dumb and not saying a word when the teacher asked direct questions of us, that sort of level. Scored diligently across a full school year, I was calculated to be more rebellious than my mate. Mods you have been warned.