On a support call with an angry customer, if they start yelling give them a, "Yeah daddy yell at me." Loud enough they can hear it but not so loud they can be 100% sure you said it. Deny everything if they bring it up and give them the most generic corporate, "we are sorry and we would be glad to help you" . They will be really calm the rest of the call and really listen to you. That or they will just hang up, either way it is a win.