The origin is from the Simpsons episode, "Who Shot Mr. Burns? (Part Two)"
Smithers: [voice-over] I left the town meeting early so I could get home in time. [in a flashback] [slurred] Ohh, I've got to run or I'll miss the opening rank-out. [a shadow approaches in front] Get of my way, please -- Jasper: Slow down. The sidewalk's for regular walking, not for fancy walking.
Smithers: Get out of my way, I'm in a hurry.

At least two variants exist: Use of demotivators style caption box, and warning sign style

Phrase can be used in conjunction with a picture of someone walking funny, slipping, tripping, falling, etc, on a sidewalk or other similar platform, to demonstrate why they ought to engage solely in regular walkin and avoid fancy walkin wherever possible.