Noogie!

The sons of Steward Denethor love each other, but like all siblings they will get into childish arguments even now that they are grown men. Even though Boromir is giving Faramir a noogie (probably going "Ha-ha!" the whole time), he will utterly destroy the person who bullies his little brother.

I picture the bash-brothers of Gondor as being a pair of trouble-makers through their childhood and youth. Starting with Boromir dragging his shy awkward little brother on quests to steal apples in the market and to play pranks on Gondor's various officials etc. Going on through the years, the two would often get into mild trouble, mainly because of Boromir's temper and boisterous attitude. bBut they would get a free pass for most things, in part because of their father, but also because they truly are Gondor's finest. Boromir is always very protective of Faramir, but deep down inside he probably loathes himself for getting his brother into trouble in the first place. Faramir is more shy and outwardly sensitive than his brother, but he is also the far more sensible one of the two. Boromir would never back down from a fight, no matter how hopeless, but Faramir knows when there is no point in accepting a challenge and when it's wisest to fold 'em. But he respects and admires Boromir so much that he's willing to join in on obviously foolish activities and face the wrath of their father afterwards. Mainly because he wants to show his brother that he is a man now, not a boy anymore, and that Boromir can quit with the noogies already.