Interpreters are regularly confronted with angry people. Most often, luckily, not people who are angry with the interpreter, but clients who argue with each other. People who use swearwords or words that you would never ever want to take in your mouth.
So, how do you deal with it? The sad truth is you have to be faithful to your speaker. If your client is angry, you have no right to tone that down, the counter party or parties have the right to know what was said in order to respond correctly.
Just remember that people of different cultures swear differently. In latin cultures many swear words are related to sex or genitals, whereas nordic cultures have more swear words relating to the devil or hell. And with new generations growing up swear words, just like slang, changes. So it may be good to brush up your swearing terminology from time to time.
This clip from Youtube shows Nicolas Farage, an EU-sceptic (to say the least), British MEP attacking Commission president Herman van Rompuy. The challenge when interpreting this is of course to trust that what you hear is truly what Farage is saying.