The act of tweeting yourself, i.e. sending yourself a tweet by sending, replying or retweeting to yourself on the twitter network.
Usually the act of "Masturtweeting" is followed by sudden realisation and an expletive, often followed by a public tweet apologising for masturtweeting in public.
@me yeah dude, I was totally wasted last night <enter>
"Oh Shiz, just sent that to myself again..."
@all sorry guys, just masturtweeted again, can't help myself