guess the real question is, what qualifies as "broken", and what's just a Quesadilla (aside from being a nice snack, the word means "little cheesy thing"

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For example, any PC who is Large, or can use an Enlarge Person spell, uses a Spiked Chain with Improved Trip.
There's a huge hole in the Diplomacy rules. Diplomacy checks aren't opposed, the PC is simply rolling against a fixed target number. So any PC designed as a "Diplomancer" can go from normal to cheesy to extra cheesy to broken in a very few levels. Consider a Half-Elf Bard (+2 Diplomacy modifier) with 5 points in Bluff (for the Synergy), five points in Sense Motive (another Synergy bonus), and a maxed out Diplomacy. Give them a good Charisma score and they become nearly unstoppable.
They start with +6, from the Racial bonus and Synergy bonuses. At first level they can take 4 ranks, and with as small as a 16 Charisma they're at a +13. Add the Negotiator feat and you're at +15. Add a Circlet of Persuasion (+3 on all Charisma checks, including skills), and you're at +18.
There is some question on whether you can get more than one Synergy bonus to this (Knowledge Nobility 5 ranks also grants the bonus), so maybe he's only at +16. You can drive that higher with a Skill Focus though, depending on how insanely they want to abuse this.
Break points for this skill, to change someone's attitude, are every 10 points, starting at 20. That means any roll of 4 or more can delay a fight or redirect an encounter. Add the Skill Focus and they can't fail, even at 1st level.
At 5th level his score is +20 without the Skill Focus. Even a natural 1 doesn't fail on Skill checks, so that first level of attitude change becomes automatic. Can't fail to get a 20, starting at Level 4.
This skill abuse actually moves much of the control of the game from the DM to the Player. That player gets to decide whether some encounters happen at all. Combat turns into pure RP, presuming the PC speaks a language the other guys can understand.
Another abuse is the Bard's Fascinate ability. It isn't a spell, it's a skill check, and as subject to abuse as Diplomacy. The total for the Perform check is the opponent's Save DC v the Fascinate. I ran a Bard whose Perform check was such that nothing short of a deity could resist. So unless your big bad monster is immune to mind affecting abilities or spells, again, the control of the encounter shifts from the DM to the PC.