I found a youtube video explaining that giraffes have four stomachs. They vomit from the forth to the second or first, and very rarely does it come up. https://youtu.be/7EXnc8SXWV8?t=70
That's an impressive superpower.
Looking harmless and then suddenly violently puke like a fire hose stream on some poor bankrobbers or something.
I bet that it wouldn't need to be some strong acid to be an effective repellent.
Maybe not projectile vomit but they absolutely could reverse peristalsis just like any vertebrate. Giraffes chew their cud while upright after all. Peristalsis is agnostic to how high it's pumping, since there is no functional loss in strength.