Is it illegal to yell and swear at a salesperson who is being rude and unhelpful?

If they are asked to leave the premises and still cause a disturbance then you can call the cops, but after the fact, it usually doesn't make any sense to try to charge them with something. If you talk to your manager about the incident, you can get them blocked from the store- if they enter, they will be immediately asked to leave and then you can call the cops if they don't. Just make sure you cover the situation with your manager. If he decides that he wants to complain to your manager or your company, make sure you've already explained the situation to your manager to defend yourself.