It does sound petty as I write this as it's only over £7 - but I was irritated all the same!
I have two cats and they need flea/worm treatment, which is prescription only. I popped into our vets on Friday to buy some and was told the cats needed a free check up first as they'd not been seen in a year now, which was fine. I took them yesterday morning. All checked, they're in good health, similar weight and the vet can prescribe the same spot on treatment for both. Great.
The vet asked whether I wanted a 3 or 6 pack for them (to be used once a month) so I asked about prices. 3 pack = £26. 6 pack = £45. So I said a 6 pack. Went to the front desk to pay and collect and they asked for £90. A simple misunderstanding, so I apologised and said i'd only meant one six pack at the moment, and i'd be back in 3 months for more.
'But which cat are you treating?' asks the receptionist with a 
face. Both, I say - i'll obviously buy the 6 pack because it's cheaper and split it between them. Which is when the problem started. From this point, I was in the vets for another 25 minutes, arguing.
The receptionist said I couldn't do that because it was a prescription medication and only to be used by the specific animal it was prescribed to. If I wanted a 3 month supply, I should buy 2 x 3 month packs, costing £52, with one prescribed to each cat. I refused. The medication is the same. I could pick up a different brand 6 pack off the counter right now and go and use it for 6 different cats if I wanted to and the fact that this is a prescribed treatment is neither here nor there. The receptionist told me that legally, she could not sell me a prescribed 6 pack knowing it was to be used for two different animals and refused to sell me anything. The vet (also the practice manager) was called out at my request.
He told me the same as the receptionist and I argued the irrationality of this and said it seemed that it was a money making exercise only. He was very brusque and said that if they suspected I was using a cats medication for another cat, they held the right to ask us to remove the animals from the practice. And that by doing what i'd asked, their records would show only one cat as having received treatment, which was 'incorrect and dangerous for the animal'. I asked if they could not just put the 6 pack on DCat1's record, with a note to say only 3 months was being used, and a manual entry onto DCat2's records to say he'd had a 3 month treatment. No, they can't, their systems don't have that capability and would be incorrect. I told them (massively irritated by this point, but as polite as I could) that I didn't really care what their records said and that was not my problem.
I ended up saying, fine - i'll buy one 6 pack for DCat 1's use only. DCat2's fleas aren't that bad so i'll leave him for the minute. Obviously rubbish. After 5 more minutes of arguing, with lots of warnings that I was only to use the treatment for DCat1, the vet grudgingly sold me one 6-pack for £45.
WIBU? I know it was only over £7 and I could have just paid, but the principle of it really got me - and £7 is £7.