i write dave mostly in his 20s so this may not apply, but also it might so! who knows!

dave, to me, is incredibly adhd and rambly. i think thats pretty easily recognizable in the way he smashes fourteen topics together in one rant or to make one point. to get this down (if you dont have this habit yourself), make sure any random shit hes bringing up isnt actually random- its gotta lead back to whatever his original point was in some way, even if his original point was a joke (imagine the structure of a stand-up comedy bit- hes doing that!).

dave can also be irritable and he def has a temper sometimes, but he shows it in a super weird way. he doesnt yell at people or directly insult, but he will get standoffish, anxious, and veeery subtly passive aggressive. the dave i write is faced with a lot of personal issues bubbling up, so hes less outright funny, but it does come through!