It is rude to have bad manners.
John is eating at a fancy restaurant with some colleagues when he feels indigestion rising up in his throat.
John wants to relive the gastric pressure he's feeling.
John excuses himself from the table with a hand gesture and turns away with a hand over his mouth, to quietly and slowly let some gas escape.
John lets out a gloriously loud and long burp that thunders over the table.
John's colleagues hardly  notice him as they continue talking and having a great evening.
John's colleagues recoil in horror as they watch their colleague act like a common animal in public.