he wasn't trying to intimidate me. he was playing. He knows better than to growl at me in a bad way.

Either stop play/interacting with them or roll em over and hold them on their back (dominate).

Loki only growls at me when we're playing tug. He gets his big mean growl on while he's tugging, but he's wagging the whole time and stops as soon as I stop tugging or if I tell him to stop.

I think if you know it's playfull, it's ok, especially if you know you are the top dog in the relationship. Any sort of actual aggression should NOT be tolerated, since it's a slippery slope.

We also play a game where I toss a sheet over his head and he gets all feisty. It's the only time he can snap at me. As soon as the sheet comes off, he has to give me kisses and be gentle. He's started jumping on the bed and getting feisty every time I go into the bedroom! It's a fun game for me to, so I do indulge him most every time. He's such a clown sometimes!