Four Sisters and Their Respective Ins and Outs

A short list of English expressions in which the speaker says the opposite of what he or she actually means but is not using any form of sarcasm:

• Tell me about it! when the speaker actually means "Yes, I fully agree with your statement and do not actually need to be told any more about said statement to further my agreement."
• You can't be serious! when the speaker actually means "I know you are serious and, though I am surprised, I believe you fully."
• I could care less! when the speaker actually means that "I care so little that I actually couldn't care less."
• I just can't believe... when the speaker actually means "It's hard to believe, but I know it's true."