If hes YOUR customer then most likely he needs you more than you need him, tell him how it is straight up, dont hold back words or thoughts just tell him straight out what you think of him. Then propose that he just try to chill out a little bit and just shut his mouth. If that doesnt work block his number and if he keeps bugging you put a padlock in a sock and bink him in the temple with it

ps. ive had many ppl who were similar, they always ruining the high, fidgiting around and just all around pissing me off, I tell em how it is and if they dont like it they can kick rocks; nothing is worse than someone who kills a buzz.