In the world we live in, there will always be difficult clients and customers. They are responsible for creating cesspool of anxiety, provoke anger, and suddenly you're forced to fantasize about what you with you could do to them.
Being in the client deliverables industry I did some research on how to deal with a difficult client. Feel free to jump in at any time.
Take deep breaths
I personally thought this was a bunch of bullshit but when done correctly it does slow the heart rate down and will calm you down.
If you can do it, walk it out
Honestly this tip doesn't apply to everyone since certain working enviroments may not allow you to do this. For those who can, go outside and take a walk around the block or just stand outside and breathe the fresh air.
Speak up in a HR compliant manner
As much as we like to simply curse these people out, if we want to keep our jobs we have to remain calm, professional to difficult consumers. Choose your word carefully and be ver specific, document EVERYTHING so you have a paper trail, use visual reminders.
If you work for yourself
If you recognize a serious personality conflict, fire them.