I think you may be underestimating the number of agents who have been thrown up on. (And the number who have had to call for cleanups for vomit that did not land on them, and medical personnel for the ill traveler, is even larger.) The thing is though, that's what they signed up for. If they can't handle vomit, they should look for another job.
From a certain point of view, it's better for the TSA agent to be soiled with vomit than it is to allow a potentially contagious passenger on what may be a very long flight.
Actually, I made no estimations at all. In this person's scenario, I would have simply enjoyed throwing up on them.
It's the little things. As he stated, the agent wouldn't let him sit down and it was over a pair of nail clippers. Perhaps the vomit wouldn't have made them blink at all, doesn't mean I wouldn't get some form of enjoyment out of it. Sounds like the agent was being a prick. Are we surprised?
From a certain point of view, it's better for the TSA agent to be soiled with vomit than it is to allow a potentially contagious passenger on what may be a very long flight.