"Yeah Right" expression

Solution 1:

"Yeah, right!" is an example of irony. Irony is the use of a word or phrase to mean exactly the opposite of its literal sense. Here it would also qualify as sarcasm. It would be understood to mean "No f@$*ing way!"

You would definitely not use it in formal writing, unless that composition was a treatise on slang or some other academic discourse on language.

Solution 2:

There's also a joke (that as far as I know can be applied to other languages as well with similar constructions; the Greek equivalent «Ναι, καλά» comes to mind for some strange reason :) where the teacher explains that there are times and languages where a double-negative has positive meaning ("Can't say I didn't see you") or it can keep a negative meaning ("Haven't done nothin!"), but there is no known case of a double-positive having a negative meaning, at which point the smart-alec of the class says:

“Yeah, right.”

Solution 3:

Alternative in formal writing could be

I strongly disbelieve that statement

or

Our company plans to take over facebook medio 2011

You: "That sounds inconceivable"