The recognition of Sunday as a day to bun (smoke weed). It normally follows excessive alcohol or class a drug consumption on the Saturday which can lead to lost puppy syndrome. It is said sunday bunday can aid almost all ailments.

When you eat dirt for the first time and leave your family to build a shack in the woods

The day of acknowledgment for the buns....aka "butt". The acknowledgment can be as simple as a pat on the butt, all the way to full blown anal sex.

As long as some kind of bun acknowledgment takes place on a Sunday, that Sunday becomes Sunday bunday.

Once the Sunday bunday tradition has started, it is expected to continue every Sunday with some sort of acknowledgment, whether it be just a verbal announcement of it being Sunday bunday (preferably when you wake up in the morning), all the way to full blown anal sex (preferably when you wake up in the morning).

Sunday bunday is the day that directly follows Scaterday.