It is another thing which comes down to interpretation. If you look at it in black and white, it is disrespectful and therefore should be a red card. However, football isn't black and white. As @zarathustra said, it depends on a lot of variables - the feel of the game, how the player has acted previously, how loud he said it etc, etc etc... For me I would be cautioning the player because whilst it is disrespectful, a player saying 'that was a shocking decision ref' is disrespectful. For me though, the thing that is different is the word "you're". I think a red card would still be harsh but I could understand the decision. It is a tough one. Would you send him off @Padfoot ?Thanks for the honest replies so far......
Would you all consider it to be disrespectful? I think it certainly is, unless clearly said as a joke........but even i would struggle with a red