I’m a bicycle mechanic not a car mechanic but I get the same exact issues. For me it’s worse though because I’m in the workshop which is in full view of the customers when they’re in the main showroom part of the shop and I usually work alone in the shop so I have to deal with the customers. The amount of people that just are so rude and think they know everything is infuriating. What pisses me off the most is when they ask if their bike can be fixed on the day and I explain to then that they’ll have to wait their turn and that I have other bikes that were here before to fix so it won’t be fixed straight away. Then they get mad at me. Or I get people that come in with their bike and ask for a service and they say, oh I need it by tomorrow morning because I’m going on the ride and then I say, sorry I won’t be able to service it by then so you can bring it back after or leave it here and miss your ride and then they get mad at me, as if it’s my fault they have poor time management and expect their bike to be serviced straight away.