Visualize a flaming blue pentagram on the individual's forehead and chant the following three times.
By this star set aflame,
I banish you in the name;
of universal harmony,
that you no longer trouble me!
As someone who has worked in the field of customer service for more years than I care to count, I've used this spell many time on angry cutomers, disgruntled co-workers, and even people on the phone! It works, with practice. By the time you've finished the chant for the third time, the person usually goes away or set their sights on another individual.
PS: If you like the photo above, its a silkscreen that one of my students made for me when I volunteered in the South Carolina Department of Corrections teaching a Wicca 101 course. I've been looking for a nice frame for it and will get a better picture of it to share with you all as soon as I do.