No bright ideas to stop his behaviors, but it might help you gain
insight to keep a log of the behavior for a week or so. Suggested
columns - date, time, what happend right before, behavior that
happened, your response, his response

This will help you identify causes and possibly see subtle differences
in your responses, leading to what works best.

When Henry was about that age, we did this with his preschool when he
was having some aggressive behavior. We realized it was happening
like clockwork at two times of the day. We experimented with extra
recess/outside play time about a half hour before it happened and it
worked like a charm.

I'm not saying the same answer will work for you, but the log is
amazing in its ability to illuminate a situation like this,
particularly when you are so frustrated yourself that it's hard to
have perspective in the moment.

He does sound impulsive... as the mother of a kid with ADD my antennae
went up... perhaps worthwhile to discuss this with your pediatrician
as well. I wish we had known Henry was ADD at that age, rather than
waiting to have that diagnosis at age 9.

Good luck!

-Dawn
Mom to Henry, 14