Throughout the show Dan has extracted vengeance on many people, most of them deserved it. It seemed like he was perfectly capable of handling the situations alone (with the aid of Chris). But if you were there alongside him for one quest, who would you have helped him get revenge on?
Personally, i think i would have gone for the Lemonade stand gang. Those kids were infuriating, i wish that Dan and Chris would have pulled a Sunny In Philly, and beat them like they deserved.
TBH i think Dan is totally justified in what he did to his stalker (dan vs. dan)... i know a lot of people are fans of the double, but it unlocked a new fear for me lol