To boast about oneself or ones succeses on the internet. Can also mean to excessively discuss something to a level of detail which comes across as condescending, constantly pointing out how superior one is in terms of knowledge, moral standpoints and so on. Usually these people need to have the last word in a discussion for example on Facebook.
"Yo man remember that DJ kid we saw the other day on tumbler, his profile all about promoting himself to fuck and no other blog posts besides that?"
"Sure what about him?"
"I posted a pix of a dude with a huge penis on his blog, maybe he realizes that way what a big e-fapper he is".

" Geez, Martin is such an e-fapper, he always has some sort of avantgarde opinion on everything or his comment is so smartass that it kills the whole Facebook thread."
by Kski August 10, 2014
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