Flash Sentry is barely a character. There's no point in trying to speculate on him because he's so incredibly bland and useless to Equestria Girls.
And that's also where Spruce Timber lies; he's what Flash Sentry should have been if Hasbro absolutely needed a dopey love interest.
DISCLAIMER: responding to darknessrising24 below, not TheWittyToaster:
Sorry to say this but while the extreme hate is going to far, heavy criticism is justified. Flash has zero personality to dicepher as a unique character.
First movie: Bumps into Twilight a few times, gets Twilight out of a dilema (within 2 minutes nonetheless) even though any other character could have done it, dances with Twilight to be nice.
Second movie: Asks once if Twilight is returning, gets annoyed she's "competing" against him in the battle of the bands, hugs her in the end.
Third movie: Is dissapointed human Twilight doesn't know him.
Fourth movie: Is dissapointed human Twilight doesn't know him, bumps into Sunset.
So basically he bumps into characters and has feelings for Twilight that are glazed over. Doesn't seem like a necesssary or likeable character. At all.
To quote Honest Trailers, "He's so edgy, he could have been cut out of the movie and it wouldn't be any different!"
Actually we would have cared because not only has MLP done this before with the opposite gender (*cough Sunset Shimmer before reformation *cough) but other "little girl" franchises have done the same thing with flanderization to the max (Bratz, Monster High, Polly in my Pocket, G3 MLP).
Nobody did. Everyone liked her as soon as "Jump up, make a sound" exploded in the cafeteria.
The major difference between the show's characters and Flash Sentry is that one, they all serve the purpose of the (mostly) character-driven show, two, they get adequate screen time to develop, and three, we actually see them act outside their advertised trait, maybe even most of the time. Flash is in no more than 3% of the entire Equestria Girls series and yet his scenes feel incredibly forced.
Please do not call those who point out obvious flaws "lazy hypocrites". We're just speaking our mind.