I understand what you are saying but pride has no value or weight. It’s an emotion that has ruined more lives then it has helped.Hello; I find some of the responses interesting in the area of priorities. Several stay focused on the value of tire stem caps and rightly so, consider them to not be a big deal. However the actual big deal, the insulting way the shop manager handled the situation, is dismissed.
As the OP stated, which I agree with, had the manager just allowed the cap may have been lost then the OP would have been willing to let it go as not a big deal. Also as the OP stated and something I also agree with, it was the treatment dished out ( the name calling and the early refusal to take responsibility) that becomes the actual problem.
I may give you things of value but will not allow you to take even a blade of grass from my yard under some conditions. I may not be able to or may choose to not do much about being disrespected, but will never let it go. I was a school teacher in KY for over 31 years and retired from there. I went to NC to teach after I retired in KY. Some of the students in a classroom in front of other students called me a mother f***er to my face. This happened several times over time before I left that school. I was very limited in how I could respond but did write them up and send them out of the room to the office. The school principal tried to tell me I was too thin skinned and wanted me to let it go. The disrespect of teachers had become wide spread in that school system. I would not and my contract was not renewed.
About the notion the OP is putting someone's livelihood at risk by making a big deal out of the small value caps. I disagree with this. The manager himself acted in a wrong way and did himself put his position at risk, not the OP. The manager made the decision to be combative and call the OP a liar. I fail to see how the OP is overreacting or being a crybaby.
Respect on the other hand is an important part of our social structure and needs to be maintained. Kids need to respect their teachers. The teacher shouldn’t take pride in the respect.
At any rate I am sure if OP showed up and talked to the guy that called him a liar he would apologize. If he didn’t respect the customer enough to apologize I would escalate it to the next level.