Wat Do?
About
"Wat Do" (or "What Do?") is an image macro series showcasing the most eccentric, WTF-like pictures on the internet, accompanied by the prompt: "Walk in. See This. What Do?" On discussion forums and image boards, this phrase is typically used to survey others' opinions or suggestions in regard to an image or scenario in question.
Origin
According to Encyclopedia Dramatica, "what do" first appeared in 4chan summer 2009, although the exact date of original instance has not been confirmed.
Spread
There are over 139 occurrences of "wat do" on 4chanarchive.
The phrase has also been found in Body Building Forums, Yahoo Answers, MMO Champion forums, Facepunch forums and more. Every occurrence found thus far dates back only to 2009. In each case, "wat do" seems to be an element of 4chan culture, used by members of 4chan while on other boards and not an element of 4chan culture that has caught on well with wider audiences.
References
Urban Dictionary
Fap Vigorously:
The best response to any "walk in, see this, what do?" thread. results in instant lulz.
-Walk in, see this, what do? (picture of spider infestation on ceiling)