can't/couldn't very well do something

can't very well (do something)

Cannot or should not do something because it would be inappropriate or unreasonable. I barely know the guy, so I can't very well ask him to do me this massive favor!
See also: very, well

can’t/couldn’t very well do something

(informal) used to say that something is not the right thing to do: You can’t very well change the arrangements now. It’s too late to inform people.
See also: something, very, well