Last Thursday 

Represents a measure of time, being the long-term memory of popular culture (and sixteen year old girls in particular), since both seem to have trouble recalling anything that happened before last Thursday.
As a span of time, Last Thursday lies somewhere between a hundred years ago and the present, and is always followed by last Friday.

It is widely accepted that anything that did not take place this week took place Last Thursday. That is unless this event took place back in the day, which is of course a Wednesday.

Last Thursday by EM3RG3NCYx March 2, 2009

Last Thursday 

When everything in the universe was created. Also, the time when many various things happened.

I started my period last Thursday.

Last Thursday by Goddess_Freya May 5, 2008

Last Thursday Effect

When you make a point that can’t be disproven or proven.

If you say God existed before The Big Bang you’re using the Last Thursday Effect.

Last Thursday Effect by FatMan1945 November 26, 2020

So last Thursday 

Same as "so ten minutes ago"

Low rise pants are so last Thursday.

So last Thursday by Liberte July 28, 2006

Last Thursdayism 

(np) 1. The assertion that all existence sprang into being this past Thursday, with all memories of sentient beings created in situ. The Universe, and everything in it, was created last Thursday, along with our (false) memories of everything that happened prior to that. Another common belief, known as Last Tuesdayism, is considered wrong.

Q: "What is the evidence for Last Thursdayism?"
A: "There's lots of pieces of evidence that prove that Last Thursdayism is true but we can't go into that right now."

Last Thursdayism by Anonymous November 6, 2002