“We may hate it but ‘Yeah, right!’ is one of the pithiest phrases in the English language. It manages to say everything in 2 words that “Excuse me, but I find what you are saying to be dubious in the extreme and what is more, I know that you know it too” manages in 26.”
Unfortunately, I wasn’t paying full attention to countdown today, so that isn’t the exact quote and I didn’t hear who said it at all. All the same, I like it 
I heard a story (doubtless apocryphal) where a linguist was addressing an audience, and he said “It is interesting to note that though you can use two negatives in English to mean a positive, there is no way to make two positives mean a negative.”
And someone in the audience replied “Yeah, right!”
But…more pertinently…Countdown ?!?!?
I did say I was fed up with being off sick! I’m not any more, by the way. Back to work now. Definitely. Can I be off sick again please?