Ridiculously aggressive clown knife?

I have a clown knife, it's about 14" and I can not keep a single living thing with him. I understand they are by nature aggressive fish and I have no problems with him. I was just wondering if this is normal, I have seen them in pet stores kept with large cichlids large bala sharks needle nose gar and such, I had hoped when he got bigger and moved to a giant tank I could keep him with some of my large sharks or cichlids but he will ault any thing with him even if they are twice his size, I even resorted to a hand full of large apple snails to help keep the tank clean and he picks them up and bangs them against the tank till they break. I understand all fish have a different temperament but wow not even snails? lol Just wondering if this is in the range of normal for a clown knife.