Elladan and Elrohir, I can buy that. Boromir is by nature friendly and honorable, and his actions in Rivendell may have been due more to disappointment with the place and his mission (sent by the Steward) than by Aragorn personally.
He also may have been a little angry in that some no name Ranger is dating Liv, while the Steward's son's off running errands and saving Gondor. Some guys have all of the luck!
PJ doesn't directly show the relationship building between Boromir and Aragorn, and skips over the same with Legolas and Gimli. I guess we're just to 'fill in' the gaps in the stories.