My gold mystery snail got along with everybody, then one day all my swords decided they wanted to try and eat him. They had been in the same tank for a month and got along fine, but then they just started picking at him constantly. They would poke at him, then when he would close his shell, they would keep biting right at the edge of his shell. It actually damaged the way his shell grows. I had to move him to a different tank and his shell still has a big line from where it was damaged. He gets along fine with my betta and tetras.
I remember someone here saying that his betta ate his snail's feelers, but I've had my snail with 3 different bettas and they've never picked on him.