Are you seeing anyone? 1: No way! 2: As if!
Did you read my diaries? 3: No way! 4: As if!
Do all of the answers sounds natural? If not, which ones are natural and/or weird and what is the difference between the two?
In your examples
is often used as a strong denial of something, and is used as shorthand for no way, jose, a kind of rhyming slang.
is shorthand for
As if I would do something like that
however context would have to built around habitual actions of the accused to support the as if!
A related phrase is
Why would I?
why would I do something like that
which is an implicit denial of the accusation and also throws back a question to the accuser.
All of those answers make sense, and you can even use both right after one another for any of these questions.
"No way! As if!" Makes perfect sense.
'No way' means that you are implying that there is no way that you could have done something.
'As if!' Is a defensive remark that pretty much means the same thing.
Do all of the answers sound natural? Yes.
No way! -> provides strong objection to what was said.
As if! -> may provide the message 'stop assuming'.