Boring Man - Online Tactical Stickman Combat

You need 2 players for this achievement (or an alt account since the game is free).

Host a server and set mutator for Permanent Triple Damage on. Equip the shield with one character and a suicidal vest with the second. Press F to put up the shield, then come with the second character, stand close to the shield and press F to explode. This should give you the achievement.

AFAIK the suicideal vest is the only weapon able to deal more than 500 damage.