Searches: various web sites, including several mentioned in previous threads here. They answer the wrong question.
My MC is a German man, age 40. He comes from a upper upper middle class family; is intelligent, well-educated, and well-read; and speaks a number of languages more than passably. (I read the fascinating mid-December thread on mistakes German speakers make in English, and he hasn't done that since he was at university.) He's currently working high finance in the northeastern U.S..
Today, a large part of one of his major work projects came apart at the seams. It's not his fault, he warned people this could happen ... but that's not going to stop him from catching the blame (and the extra work) for the next month or so.
So he gets home and, instead of putting things neatly away and kissing the wife, goes to the living room, pours three fingers of Obscenely Expensive single-malt. knocks it back on two gulps - and throws the glass into the fireplace as hard as he can.
At this point he allows himself one sentence to vent, and I think it should be in German. I'm looking for something like
"God damn yellow-bellied illiterate needle-dicked squirrel-molesting disease-riddled son-of-a-BITCH!"
as opposed to more ordinary profanity. (Ergo (in part) my comment about answering the wrong question.)