It's obvious that Dave is really fucking cool. He jeers at John's inability to set up his Sylladex's Fetch Modus when John asks him for help and berates John's interests constantly. Dave is much more skilled than the other three characters, who either through their own cluelessness, admission, or silliness are less capable than he is. Through the conversations of Pesterchum and his own introduction, Dave already has his Strife Specibus set and he has one of the most advanced Sylladices available, giving him a huge advantage over the other three characters. Jade may be able to maximize the use of her Sylladex due to her precognitive abilities, but under normal circumstances it'd be close to entirely useless.
His incredible coolness also enables him to stay level-headed when dealing with supernatural things, (like Sburb) incredible things (like Meteors or Time Travel), or generally disconcerting things (like seeing his own corpse or talking about his dead friends).
Despite being the coolest thing since the Fluffer Nutter, Dave seems to be easily influenced by John. He has never removed John's gift, citing irony as the reason, and John's talk of the monster Howie Mandel stopped him from enjoying his Apple Juice. Also, it is important to note that Dave never feared his brother's puppets until John pointed out how unnerving they were. It might be that Dave is just an easily influenced person based on his inner desire to be super cool, but he has no problem keeping his distance with Rose.
Dave is a bit forgetful. He always loses his place in the latest MS Paint Adventure, sets several Sylladex traps, only to release them on himself moments later, completely forgets to pour out some Apple Juice for his homie, forgets all about his Timetables and thus, forgets he can go back in time, and even manages to forget his own intentions to forget something. (though that one might be him being ironic again)
Dave keeps a calm facade up to the exact moment he flies off the handle. This has happened when something makes him look stupid, like being buried under a mountain of puppet dick or having crows invade his personal space.
Underneath his cool facade he appears to be rather caring towards animals; he was visibly upset when he accidentally harmed a Rambunctious Crow and he may share Jade's interest in anthropomorphically persuaded fauna. However, this might just be one of his many ironic gestures. Regardless, his gift to Jade - a picture of Sweet Bro and Hella Jeff as furries - seems pretty sincere.