I walked into the room to catch the last part of Piranha!
It's totally unfair to evaluate a movie when you haven't seen the whole thing: I missed the setup that made this a logical and gripping drama, deeply symbolic of something or other. Maybe. As it was, I watched the snap and flash of teeth, gagged at gallons of fake blood (Girrls-N-Gore!), and wondered... why not just get out of the water?
I also recently re-watched Tremors. THIS is a B movie! The premise - giant toothy-earthworm monsters track folks by vibrations of footsteps, then pop out of the ground to eat 'em - is far-fetched, but not illogical. The dialogue wouldn't make Shakespeare give up his quill pen (maybe snap it?) but it's cheesy fun. The film romps along with such verve and humor (and such helping of young Kevin Bacon) that you can't help but enjoy the whole lunatic thing.
I recommend Tremors with an extra-large non-buttered popcorn. ('cause, if you throw popcorn at the TV, butter smears the screen.) Enjoy!