Meat don't wanna cook
This is strange but I don't know what to do.
I opened 2 packs of ground beef tonight to make a bunch of recipes for the weekend and I cooked it like I always do, in my non stick pan with a bit of salt and pepper.
Problem is that the meat look cooked, it's brownish but some bits of meat, they are still pink, like uncooked.
So I put it back to cook it some more, and despite leaving it for a while, despite the meat starting to dry from heat, it's still pink!
What would cause that?
it's possible that some of the meat was exposed to either nitrites or carbon monoxide.
In normal, raw, meat myoglobin is bound to oxygen which produces a red color. When meat is cured with nitrites, nitric oxide bonds to this point instead of oxygen setting a pinkish color that will not change significantly when cooked. It is also possible for carbon monoxide to bond to myoglobin to produce a stable pink coloration.
Most likely what happened is that your ground beef contains bits of corned beef or maybe even ham or bacon. A butcher shouldn't really be adding cured cuts to the ground beef scrap pile (!)
source: on food an cooking, harold mcgee
"ground beef contains bits of corned beef or maybe even ham or bacon"
If what you wrote is true, which I believe to be the case, it's time for the OP to find a more reputable butcher. Bits of corned beef, ham or bacon are not bad things, but adulteration of a food product without proper labeling, which amounts to disceptive sales practices, are.