Some sort of search query easter egg: for example when you hit "sloan" we will show you some video with sloan, i don't know... that's stupid.. but you get the idea :)
In the /settings/profile, when you choose two brand colors that have poor contrast, we could show some funny gif
Another GIF if you try to set your font to be Comic Sans MS
I'm sure you know the Dinosaur game in Chrome when you're offline.. Maybe something similar? Although we do have a drawing board already...
Choosing 10x hacker theme would activate matrix code in the background (only once :P)
Some funny HTML comment hidden in the source code?
Some random ideas..s
Comic Sans MS
I think clicking the footer mascot should do something— possibly something configurable by forem creators
I loved what Kickstarter had while ago for footer: