It's rude to be short with someone.
John who is irritated about something is walking around the office when Sally tells him to have a great day.
John wants to respond to Sally's statement.
John tells Sally thanks and tells her to have a great day as well as he walks away.
John tells Sally to buzz off and keep quiet since it's quite the opposite of a great day.
Sally is happy John reciprocated the well wishes and goes on merrily working.
Sally is sad that she just got snapped on and a little scared and goes silent for a while.