An upstart is someone who's cocky and arrogant, and who doesn't show much respect for other people.
There are many ways of starting up trouble — one is by being an upstart. Upstarts are people who are full of themselves and dismissive of others. Often, an upstart is a young person or newcomer. A new employee who acts like he knows more than everyone else is an upstart. An arrogant rookie on a sports team is an upstart. In the 1500s, upstart and start-up were both used to mean the same thing, "one newly risen in importance."