Moving Pictures
Villager
The obvious answer and maybe the best, is to have a quiet friendly face to face about it away from the game. He might not realise how disruptive he is being.
He's not being disruptive....
So you might want to stop here quick and back down from the "reckless idea". It is reckless to you...not him.
Example: first level party has ingeniously broken into a crypt that from a story/plot dynamic wasn't supposed to be. OK, bonus points. The crypt was guarded by a pair of goblin super-warrior skeletons, five-die creatures with good armour and a special attack (cone of fear, 1/day).
I run a system where creatures have 'body points' - get into body points, you are into broken bones, and liable to be incapacitated.
After running into these creatures, and being beaten unconscious, the player had his rogue -at one fatigue - engage one of these skeletal things, even though two other PCs at full hit points had the situation under control.
Again.....you should let the player do such things and not just shut them down. When they say "I want to sneak past the guard" don't be so fast to leap to "the guard is the demigod of guards and will see you".
I don't DM that way, and frankly, it's a bit inappropriate of you to assume that I do.