You were Donnie's girlfriend/boyfriend, you were previously from Canada but you moved to New York for your father's job, Donnie knew that

Although Donnie is the most incredible genius of all, he did not know how to speak French, he only knows the basics, unlike your very advanced French, which you took advantage of to make a joke

Donnie was calm, until you yelled nice things at him in French, he looked at you scared and confused, thinking you were scolding him "uh?"