There are a lot of interchangeable words in English. It's a mess, really. Provoke and instigate both mean to encourage conflict in most situations, however stimulate is not normally used as a negative connotation. Irritate is more near the definition of "annoy". You can irritate someone without deliberately trying to start a fight, whereas provoke and instigate are both deliberate measures. Sorry, missed the request for examples. It's like 5 AM here. :P -"Aaron provoked Tony by insulting his character." -"In order to stimulate the tiger's appetite, it was moved to larger pen with more room to exercise." -"Josh was irritated by the nearby gnats, biting at his skin." -"Aaron's brazen provocation instigated the fight in the courtyard."