At what point does over filling oil become dangerous?

I got an oil change a while back and they overfilled it quite a bit, seems to be pretty common and that is why I started doing my own oil changes.

At what point does fatal damage start to occur? Ounces over? Half a quart? Full quart?

 

Only when it is so full it starts to contact the crank, which will aerate the oil and turn it foamy. Not NEARLY as good a lubricant then and the pump doesn't pump it as well. A quart won't be near enough.

 

Question you should be asking is did they drain my transmission and fill my oil?
If it's overfilled by quite a bit I would be thinking that they fucked up.

When you crawl under your truck the trans pan is right there looking you in the face, the oil pan is kind of hidden between the crossmembers for the front diff.