Okay, we have a clarification issue here. Our Barbarian has Unexpected Strike. A rogue enemy used Acrobatics to tumble around him. You can use Acrobatics to avoid Attack of Opportunity. Unexpected Strike says you get the AoO when they enter the square regardless of whether it would normally provoke.
Our Barbarian is arguing that Unexpected Strike trumps Acrobatics (I'm inclined to agree. I feel something you have to work towards getting and that has so many restrictions should trump a standard skill.).
The DM argues that Acrobatics avoids AoOs and would avoid the AoO gained from Unexpected Strike.
Thoughts? Opinions?