there were pained expressions and then the PI "responded" by just repeating exactly what he had just said before my comment.

Sorry to be off-topic, but:

Even after consulting this list, I can't come up with a single meaning of "PI" that would make sense in this sentence. ( "Principal investigator" is perhaps the closest, but that would only be appropriate if you are a research scientist and everyone here knows this, likely because they're research scientists too.)