You drank my drink!!

So we had a deal on our cocktails, Buy one get one free but you have to have one pornstar and one espresso martini. This Karen comes to the bar and wanted two pornstars. I said you can but the deal is for one each! she moaned to her friend for a bit saying she doesn't really like coffee and then agreed she will have one of each! She sat down then within 2 mins storms back to the bar, slams the coffee glass down saying it tastes like shit! (Don't know what she does in her spare time!) I explained that we sell a lot of them and we haven't had any complaints. She asked me to taste the drink, I said I'm not allowed to drink when I'm working. She said smell it then! I smelt it and it just smelt like coffee! Then she demanded she wanted another pornstar (Like she wanted in the first place) I said I can't sorry, She then demanded the manager. My manager came and she was shouting at her telling her the drink was off. She poured a bit more of the cocktail for her and she said that was better, The manager said well it's exactly the same and we can't change it! The Karen then said she needs a new one as I apparently drank her first one and it's health and safety !!!! My manager asked me if I had drank her drink (She knew I wouldn't of done) I said no then all hell broke out she was swearing and shouting at us saying we have contaminated her drink! In the end my manager asked her to leave as she was causing a scene in our venue! What the Fuck is wrong with people!!!