Do people with bipolar snap easier when they are upset with someone?

They can. First, mental illness is quite common affecting around a quarter to a third of the population. Secondly, most folks with mental illnesses are not particularly violent. Next, it is true that a person with bipolar disorder may become irritable and volatile while their condition is not well controlled. Additionally, not all with that diagnosis actually have it. Finally, we should help those with it.
Snappy Bipolar. Bipolar people in a manic phase who are non-compliant with their medications or are abusing alcohol or illicit substances can sometimes get irritable & snappy.