Atchoo!
We have come to the point in our lifetimes that doctors are now suggesting we try playground tactics to deal with life. Sneezing on someone is an incredibly rude thing, but sneezing back at a jerk won’t fix it or improve life in any way. So don’t do it.
Needless to say, the patient can’t be blamed for not being amused, especially given they were already feeling absolutely awful from a bad flu to begin with. There’s a time and a place for humor, and if that was the intention, then and there wasn’t it.