One difference between a comedian and a joke is a comedian isn't usually
desperate to get respected or taken seriously. Another difference between a comedian and a joke is a comedian is not
desperate to come off as someone with a sense of humor. Yet another difference between a comedian and a joke is a comedian doesn't usually try to come off as more than a comedian (sex symbol, action/war
junkie, athlete/jock, political activist/world leader, rock star, martial arts fighter, assassin, and so on added on as extra for some comedians).
The comedian just makes
people laugh, he/she doesn't claim to be the underdog comedian, the comedian who tries to do work in five different areas so the
people who laughed at him would take him seriously, he/she just makes
people laugh which is why he/she is funny and some jokes are not.