that has the same meaning as the phrase
"It's Water Under the Bridge"....I guess. You should
use this after
an argument. It means that something happened in the past and can`t be changed. You see, once you squeeze toothpaste out of it's proper tube, the toothpaste cannot go back into the tube. You can get a toothpick and try to push it back into the tube, but I'll be Goddamned if it wont
go back, and if some of it does you have, at best, an awful mess.