Know something full/perfectly/very well - Idioms by The Free Dictionary
know something full/perfectly/very well
know full well
To know or be aware of something without any possible doubt. You know full well why I'm upset with you, so there's no use playing dumb! We know full well that many families are struggling to make ends meet, but these tax increases are unavoidable.
know something ˌfull/ˌperfectly/ˌvery ˈwell used when you wish to indicate that the person you are speaking to already knows something you have just said or are about to say: You know full well that smoking is forbidden in this room. ♢ You know perfectly well what I am referring to.