1321. Tell everybody that "1337" is leet, as in leet speak(using numbers/symbols to represent letters, 1!k3 7h!s). I'm surprised nobody knows about this :P. Maybe I just spend too much time on the internet.
1280. Tell zellinkda it's when you're making a post but somebody else posts before you, and you don't realize it until you've made your post, and it's really awkward.
And might just happen to me right now.