Just today! I do alot of vehicle "safety insections" among other things in my "line" of work. Drove a jalopy on to the rack. After confirming the operation of brake/shift interlock, low, high, turn, tail, brake, and reverse lamps, wipers, windows, door locks....I turned the vehicle off, opened the driver door (triple checking to ensure it was INDEED unlocked before closing the door (key fob was in the vehicle as well) I stepped to the left passenger door, opened it, checked the operation of the child lockout feature, tugged on the seatbelt to check the locking feature, shut the door and made my way to the liftgate to check the spare tire, jack, tools, and presence of road triangle. My hand was 1.72 cm from making contact with the liftgate handle and I hear a KUH-CHUNK. I find myself in a classic lockout scenario. Customer vehicle on lift, locked with keys inside. If I was younger, I may have panicked with that hot sweaty feeling. But I'm older and expect this kind of stuff, really. No surprises, anything possible. But had a definate WTF moment. Luckily owner in the lobby had a spare "fob" on his person. Problem solved, we had a good laugh.
5 minutes later, next vehicle. In-cabin checks, GO. Get out check the left passenger position stuff. Move to rear of vehicle for that stuff. Open the liftgate. As soon as it opens to a distance to allow what fell out to fall out, BOOM, half-rack of Sprite falls out, busts a can and starts frothing on the shop floor. Exactly what you don't "need" to happen. So I was just like, what's next?
Well, never trust the customer, right? Even though you do, yeah?

So I tear down the rear brakes on an '18 Ford Transit 350 Turdmobile for a pads and rotors R&R with customer supplied parts. Only I don't check the parts first. You gotta pull the axles to get to the rotors, so luckily I wasn't so dumb that I went that far before checking. Anyways, totally front pads and rotors in the box. So it's on jack stands and I play diplomatic texting tag with the customer throughout the day trying to professionally say, "Yuh done ordered the wrong crap." Pictures and everything. Being where I'm at, parts mix-ups are 2 to 3 weeks in sorting because everything comes on the slow boat.
But whatever, stuff happens. I work at a hobby automotive shop where I play more of roaming advisor for DIY types. Then a little light maintenance and repair work as agreed to with the customer and prices/labor rates are very reasonable. It's not like doing flat rate warfare at an independent shop or death-by-warranty/recall stuff at a dealership. I'm just whining, really.
Hope you're doin' something fun.