poor customer service

As a regular patron at this specific spur because we were always looked after, the manageress has not only left a sour taste in our mouths but we will NEVER return to this establishment again. After ordering my food and drowning it in sauce (as I always do, spur sauces are yummy) when it came to my second last bite I saw black snotty , slime lettuce that was on my burger. I showed the waitress and said im not making a huge fuss about it but that she must bring it to the attention of the griller so that other guests don't have the same experience. No big deal! UNTILL the manageress came to the table to tell me that it was onion!!! Really??? Black snotty onion???? I was not causing a stir so no need to come to my table and insult my intelligence??? Apologize fix the problem and move on!!!!!!! One persons arrogance has cost a regular customer. The other manageress wanted to remove it from the bill but I insisted on paying for it seeming I had eaten it. Her approach was more what you expect when it comes to customer service so well done to her. I would like to reiterate that its not about the food, Its how it was handled.