Some people cannot get by without a tickertape parade for getting you a fresh pencil

An assistant should know the role and the place of an assistant They are not a wife or mother though many assistants or secretaries take on role of mother wife protector and archenemy

Rather than encouraging further tension with "Thank you" only maybe a private discussion about conversations in front of colleagues and other co-workers is in order and include in that discussion that ones attitude as an assistant is not intended to be that of a manager or superior

By all means help them to feel like a valuable part of the team and appreciate their contribution and if need be explain that you had certain things on your mind which were more important to you than the appointment though you do not need to elaborate Wishing you well with this situation