Not all true though ignorance might be a good solution...

no one wants to be called a "snitch" but if that person is affecting your work performance then write down all the stuff that person said to you(any witnesses,time, etc)
and then talk to HR...(Many of the companies have the handbooks for this kinda things so maybe try to read the rules etc...)

In the meantime, spend as little time as you can with this person as possible...