Intonation is Relative
Andrew Hitz
"It is okay to play out of tune. It is not okay to stay out of tune."
-Michael Davis of (Hip-Bone Music and Former Trombone Player for the Rolling Stones)
This also brings to mind one of my favorite phrases: "Intonation is a social skill."
If two people are playing together and are not in tune with each other it doesn't matter what the tuner says. One is not flat and the other sharp. "They" are out of tune.
Whether you are "right" or "wrong", when you notice you are out of tune, fix it.