A Semisult (alternatively, halfsult or hemisult) is the first half of an insult, although frequently it is mistakenly regarded as a whole insult by itself. But without the application of the second half, there is no real insult.
The truth about insults is that they are taken, not given. The last time I was in Morocco a group of children shouted at me in Berber, a language I don't speak. They might have been verbally abusing me for all I knew! But did I feel offended? Not in the slightest! Why? Because I didn't convert their words into an insult in my own head. I didn't provide (through my own volition) the second half of the 'insult'.
And that essentially is how an insult works, that's the mechanism: it's the person who feels insulted, not the person who casts the 'insult', who completes the insult, who brings it into being, who makes it a proper insult. Without the contribution of the insultee, there is no insult. There is only a semisult. In fact the insultee (or semisultee) is more responsible for creating the insult than the insulter (or semisulter). If it ever became the case that insults were made illegal, it is the person who feels insulted who logically ought to be arrested.
Writers and hacklings semisult each other all the time; almost always the recipient of the semisult provides the second half of the insult as a reflex.