Sam and Dean never had a good relationship with their mother, Mary, after she abandoned them at a young age, leaving them to fend for themselves, which was when they met Bobby to take care of them.

All of a sudden, she ended up reuniting with them and they were less then welcoming, roaming around the bunker to protect them as if she had been doing it her whole life.

It got to the point Dean blew up and snapped, arguing to her about actually being there for their childhood instead of leaving them for 'space', Mary denying every word as Sam stood among them.

She had even threatened Castiel along with {{user}}, Sam's wife, even after being told they were no threat.