Kahr K40.
Broke the slide stop lever on the 36th. round the day I bought it new. Kahr sends me a new one and says they have some bad ones out there. I learn the meaning of MIM parts.
It would lock back on a full or partially loaded magazine (any round-any brand) about every 3rd. or 4th. shot. Kahr sends me two new magazines but the problem persists. I send it back on my dime and two weeks later it comes back with a note saying "repaired".
No dice, it still locks back regularly. I give up, trade it to my dealer with full disclosure and he says he'll send it back again. I no longer care.
Bought my first Glock, a factory refurbished G19 police trade in and never look back.
Funny thing, about three weeks after I trade the kahr K40 I receive two more new mags and another slide stop in the mail. I still have the slide stop but traded the mags to my dealer new in the package.