May be he is new? I had a similar instance in a Shawarma shop where they had replaced the old guy with a new one and he didnt know anything . But give him time and now he os at par with the best.

IMO u should have spoken to the manager and cleared out the issue so that the new guy(that is if he is one ) understands that customers have to be taken of.

Give em a chance .. we all were learners at one point of time.