Very interesting that you consider uttering a racial slur as one of the worst scenarios that could occur to you while standing in line at a coffee shop.
So for his exposure therapy (after a considerable amount of work to get to this point), our therapist had him go into social situations and do some harmless stuff to embarrass himself to learn not to really fear it. One example was like rambling gibberish while in line for coffee or awkwardly dancing while waiting at a crosswalk where passing cars could see him.