mad dog keen
When you're so ready to do something stupid like surf, drink, or punch someone that you're like a dog who just got a bone and won't let go.
"I'm mad dog keen, I'm gonna surf even if I fall into the ocean and get eaten by a shark."
He was mad dog keen, so he drank the whole bottle of beer in one go and then started yelling at the moon.
She was mad dog keen, so she jumped into the fight without a plan and got knocked down.