The Quarians are a race of Immigrants who fly around the Galaxy in a giant fleet doing absolutely nothing productive. Instead they fly to planets and steal hard-working citizens' jobs. They also strip-mine everything in the system before they leave. It is because of these traits that the Quarians are known Galaxy-wide as a bunch of assholes, hated even more than Humans. Wow.
Another thing they did is to create a race of robot slaves and then tried to wipe them out simply for asking how to do something. They used to live on a Giant Garden but their Gethies took it off them. Ha. They had to wear suits from then on becuase they have failed immune systems as a result of their home planet being devoid of insect life. How unfourtunate for them. They are very afraid of nasty germs and so an easy way to terrify a Quarian while onboard one of their ships is to simply threaten to breath without a mask. The thought will have Quarians quaking in uncontrollable terror and they will undoubtably bow to your every command.