Word or phrase for "i'll do __ if __ happens"

I can’t seem to remember this word. It’s uncommon and is used to refer to the promise that "if ‘some unlikely event happens’, I’ll do ‘something well outside my comfort zone that I would otherwise not do’".

For example, a lot of college applicants say "If I get into Harvard, I’ll ask out this person" or a professional may say "if I land this client, I’m buying a Porche". What word would refer to this?

To clarify, this is not simple hyperbole. The if-condition, while unlikely is not impossible and the then-clause is expected to be fulfilled if the if-condition is met.

Not sure if it’s a single word or phrase, so I’m leaving both tags in