Tell Me What You Really Think

Since I came to the conclusion that I most likely have Asperger's Syndrome, I can finally come straight out and ask a question that's been bothering me for a long time. One of the hallmarks of Asperger's is that you can't pick up on nonverbal language cues and you're stuck with trying to figure out what expressions mean based on how other people react to them. Most common expressions I've heard before and I've had ample time to figure out more or less what they mean and how rude they are. But there's one that I was first exposed to only a few years ago, and that's "Gee, why don't you tell us what you REALLY think?" This is said after someone has just disclosed a forthright opinion. When I encounter it in conversation, I do the best I can to react in a normal way. I've never seen it said to other people so I don't know how they react, but it's been said to me many times. If I could just see how other people react to it, I could copy their reactions.

I cannot for the life of me figure out what this phrase means. Is it a sarcastic way of acknowledging the forthrightness of the opinion? Is it a way to "push back" at someone who has just given out way too much information about their opinion? Is it a reaction to impoliteness? Is it itself rude or polite? Is it a not-so-gentle way to remind people not to say every word that goes through their heads?

Please leave your response in the comments. Thanks.