There have been many times in the history of Smash that stick in the mind - I've just picked a few of the ones that I remember (plus the london bombiongs which was just before I started posting ut is obviously a big thing) but there have been many more that for different reasons stand out to different people - I'll always have a soft spot for the arrival of Umage...a whole page of "Is that Jamal?" posts in about 3 minutes...but there's also Dis-X, the league tables, the birth of Glasgow gets smashed/ Manchester gets smashed, the lockdown, Goodygate, feuds, departures and returns...something for everyone.
Same deal as usual...don't just pick one, say why, and if yours isn't there, then pick "Other" and say what it is...just say why it stood out for you.