I DM a D&D campaign mostly built on 2nd Edition. One of my players, who is also my friend, has a character that has become a problem, but not in a social way. His character is funny and doesnt' do anything to aggravate the others, but he recently hit level two, acquired a set of pretty decent armor 9field plate, and he also has a High Dexterity Stat, meaning his armor class, the thing that defines how hard it is to wound/hit you, is nuts( AC -4). I doubt I could find any second level monsters or encounters that would have his armor class or have any decent bonuses to hit, without the rest of the party being absolutely destroyed with him standing there not taking hits. So one option that presented itself to me was to fudge rolls without him knowing, which wouldn't work long, since he knows Ac -4 is godlike, especially at 2nd Level of all things. Another was to just throw monsters with abnormal bonuses to hit against the entire party, and make combat unfun for everyone but him.

The last resort is to lower his dexterity bonus to armor while he wears anything heavier than chainmail. I don;t he's particularly keen on that idea, when I last softly suggested it to him, since he went the book for proof that field plate doesn't affect his character's Dexterity to that point. The thing is, even with the reductions I would give him, his AC would sink to AC -1, still something that 2nd Level Characters would drool over. My reasoning for that reduction is that you don't bob and weave like a fencer, (which his character is partially based on) when wearing field plate, since the strength isn't in movement, its in brute protection. You take a fencer pose and you expose joints and openings, jumping back and diving around like a gymnast will do that as well. I'm not sure how to break it to him, without being to rude or appearing demeaning to his effort to build a really cool character. Any help or anything to suggest?

Just personally, have a thief take it in the night. Or damage it so the buff is lowered.

He can replace the armor. The armor isn't the issue, it's him wearing field plate at level 2 and having huge dex-based armor class bonuses. I think If he blows me off on my reduced Dexterity Bonus while wearing armor, I'll just write his real AC on a slip of paper and fudge rolls that way. There's no way he's getting hit without the encounter's getting lucky on rolling against him, and there is no reason I can see why he should be way tankier than the dedicated meatshield for the party. He's a warrior, but more of a control warrior. I'll just take him aside and let him know. Plus I still have to go through his character sheet to make sure he isn't fudging anything. He uses a whip (a dex based weapon) and was adding damage from his modifiers to it (a no-no, only strength based weapons add damage to hits). I need to make sure he isn't cheesing stuff without me knowing anyways.

For that, I am lost. Sorry.

He'll still have an AC to die for, just not as unhittable as a full size DRAGON's armor class.