Same thing happened to me a few weeks ago. I needed new tires put onto my wheels so I brought it over to Tires Plus. I specifically asked them if they used a torque wrench or something similar to tighten the wheels and they said YES. Next time I took the wheels off, the lugnuts were almost impossible to take off with a normal tire iron and one of the lugs snapped. I then brought it to a local garage and the replaced it for $40 I think.

Arent the wheels supposed to be tightened with a certain amount of ft lbs of torque?
If they are overtightened, can the cause brake rotors to warp?