Mad Keen - Being mad keen means you're so eager to do something, you're

Being mad keen means you're so eager to do something, you're ready to take a punch for it.

I'm mad keen on this game, I'll take the first punch if you want me to.

She's mad keen on this drink, she drank the whole bottle before the bar even opened.

He's mad keen on this surf trip, he packed 10 surfboards and a tent for one person.