It's rude to humiliate someone in front of others.
Frank is hanging out with a group of fellow students and no one is paying much attention to him.
Frank wants to be liked and noticed.
Frank tells the group a funny joke he heard the other day.
Frank points out and laughs at an embarrassing stain on another student's shirt.
The other students find Frank's joke hilarious and form a positive impression of him.
The other students find Frank's ridicule to be rude and forma a negative impression of him.