Pigs Fly 

Its happened: Cops in helicopters.

When pigs fly!
They do.

Pigs Fly by Zach G. November 14, 2003

when pigs fly

never; it won't happen

F student: Think I could get into Harvard?
A student: When pigs fly!

when pigs fly by William MacCabe December 28, 2005

When Pigs Fly Virus 

The 2009 H1N1 Virus which is believed to be made up of Human, Swine, and Bird parts.

The chance of getting this new virus from pigs, birds and people in the spring is about one chance in a million. I think that's why we call it the when pigs fly virus.

When Pigs Fly Virus by Tomicus May 10, 2009

International When Pigs Fly Day 

The first Wednesday of October, farmers around the world climb to the tops of their barns, strap wings on a pig, and throw it down onto a mattress.

Howdy, y’all! Get your porkers ready, because it’s International When Pigs Fly Day!

International When Pigs Fly Day by TheMoosetopian November 1, 2021

when pigs fly

Sacrastic sentence suffix to indicate non-adherance to the subject in hand.

Sure I'll pay you... when pigs fly!

when pigs fly by Gumba Gumba February 25, 2004

when pigs fly... 

A statement made when somebody mentions the improbable.

Lame Person Who neithers Bathes nor Thinks- Duuuhhh...so when can I get your phone number?

Me- Oh, let's see...how about when pigs fly?

when pigs fly... by RatchetBoo June 6, 2003

when pigs fly

A not so subtle reference to Attorney General William Barr flying all over the world to investigate “Deep State” politics and international connections to it.

Of course it is entirely improbable that Attorney Generals travel all over the world to look into screwball conspiracy theories, but AG Barr has made the improbable come true, so we can now say “when pigs fly” and really mean it!

when pigs fly by Dr Bunnygirl October 7, 2019