Again. If you can show me where 'fapping' is used to mean anything other than masturbating, I'll reconsider.
Only if you first show where the definition of a valid euphemism is that it has more than one alternative meaning.
eu·phe·mism
n. The act or an example of substituting a mild, indirect, or vague term for one considered harsh, blunt, or offensive:
My contention is that if the word or phrase substituted can still only mean the harsh, blunt or offensive word or phrase, then it is not a euphemism.