I agree, there were soooo many rights of passage in the game.
Like getting Vazilok disease.
Or getting killed by a sniper on your way to a mission.
Or forgetting that you were on a team, and opening a present.
Or trying to get to the mission door in the hollows or PI with purles lurking about.
Or getting gang-shanked by a horde of alien monkeys.
Or jumping off the tallest building in Paragon City.
Or kicking enemies clear across the map. 
Or fighting a group of Helions in Atlas Park as a level 2 or 3 and having a level 4 come to "help" you.
Or taking the wrong stinking train in Steel or Sky and mistakenly clicking Talos instead of Atlas, as a level 11
Or getting griefed, (higher level ambush abandoned and you get targetted).
And some good things too
like standing on top of the Atlas Statue
Or getting the beacon for some zone and setting up the telepad for your SG base.
Or getting the 4 accolades in the game, (though not as helpful as they could be)
- Task Force Commander
- Atlas Medilon
- Portal Jockey
- Freedom Phalanx
Or seeing / hearing something silly like
Somebody had a toon named "Capt. Color Blind" and he loved to go to the tailor shop just to cause an NPC passerby to say, "Nice threads, Capt. Color Blind". Now that's high comedy.
Or seeing strange things in-game, like those office workers in City Hall in Atlas park walking up and down invisible stairs in the middle of the lower-level hallway.