Crap excuses in general wind me up, but the stuff that winds me up even more is when people claim to have done nothing wrong or not have forgotten something but yet somehow magically the problem is solved when you get off the phone to them.
One example: a parts company we deal with for warranty work and general supply of manufacturer specific parts has just changed to an online/email only invoice system. No problem, I filled in all the details online. Set up my account, received emails to confirm my email address etc all fine. Months later I try to log in to their system after some warranty work was carried out at the same time as a service. Can't log in so I email their tech support guy from the info provided on their website: no response. Call their offices, leave messages, nothing. So I leave it figuring that when they want their money they will have to chase us for it the old fashioned way- with a standard paper copy.
Eventually we start getting shitty phone calls and "final demand" letters from their credit controller for having not paid the invoices they have sent. Fair enough, we haven't paid so I ring them to explain/pay the bill- no answer so I leave a message asking them to call me back giving them four different numbers they can contact me on, plus my email address. I also email them and try to log in to their system again using the details I previously supplied on the website they provided in my registration confirmation emails. Email not recognised apparently so I email and call them again, still no response. I finally get hold of their credit controller and explain that I have tried repeatedly to log in, contact them and attempt to pay for these parts but have had no response. She FINALLY picks the phone up and says "well they have all been emailed out to you". I check my email once more and scour my spam folders again just to make sure- nope, nothing there. She then tells me I must have put my email in wrong. I explain that this can't possibly be the case since I had confirmation of registration emails- which I have forwarded to her! She denies all knowledge of my email and my registration (read: she lies to cover her arse) and says that's no one ever received my phone calls and emails despite me being able to prove that I did carry them out or send them. I provide her with my email address AGAIN and ask her to email me the documents over in order for us to pay the invoices- she does and I notice that my email is missing the "L" off the end of hotmail. I explain that it must have been copied over wrong as I got registration and confirmation emails but nothing since. She denies it and says that I will have to register again. Try, can't do it as email is already registered (despite previous attempts saying it wasn't recognised).
3 weeks later I magically start getting the invoices emailed to me through my account. No word from them, no explanation no nothing. It really winds me up when people argue that black is white, realise they're wrong but instead of saying "sorry I've just seen it wasn't copied over right" they carry on denying all knowledge and then just fix it on the sly and never even mention it. Really winds me up!!