I'm in need of some synonyms

I’m looking for phrases that are similar to “when hell freezes over.”

When pigs fly…

um…I’m coming up with major brain fart here. Who here can help me out?

“when monkeys fly out my butt”

“when donkeys fly”

“sine die” - pretty pedantic one

“never in all one’s born days”

“on the second Tuesday of the week”

“not in a month of Sundays”

“when the moon turns blue”

How about “when manny leaves an IMHO thread in GQ?”

When Cher suurenders to gravity
When Martha Stewart wears polyester
(sings) Until the twelveth of never, and that’s a long, long time…

I don’t know if this counts, but it is what I always say:

not in a million years

Thanks for the replies so far. I’m trying to gather a few of them for an e-mail I’m sending to my friends about an impossible event that just happened.

BTW, manhattan I thought about IMHO for this thread since it is a poll of sorts. But the question I’m asking had factual answers and so I decided to put it in GQ. Oh well.