I found this phrase "Please leave the tomatoes at home" in an email. On searching online I found it used in several places which are related to inviting people for an event.
What exactly does this phrase mean? I am guessing it's meaning to be like "come without any things which can be a distraction for the event happening"
Jim's comment is accurate. it means "come with good mood" - bringing tomatoes with you to an event means you expect the event to "suck" and intend to punish the event organizer/performer by throwing tomatoes on them.
This is the same practice referenced in the name of the movie review site: http://www.rottentomatoes.com/
The suggestion is that your review might serve the same purpose as tomatoes you would have thrown.
The practice was common during the Vaudeville era, a time when over half the US population were farmers, and before movies and TV displaced live performances. Stand-up comedians still reference throwing rotten vegetables, their form being basically unchanged from their Vaudeville predecessors. So it is an interesting result that comic TV and movies seem to most reliably represent this practice. Everyone from the Marx Brothers to Robin Williams is represented in TV Tropes excellent list of examples:
