Indeed, he and Cullen are such close friends that Hines took delight in poking public fun at his former captain's looks in the build-up to last week's game.
But their friendship will be parked when the whistle blows today. When Hines crouches in the scrum in front of Cullen he will not be looking into the face of a buddy. All he will see will be a blue-shirted opponent who must be dominated.
This emotion will be shared.
Cullen is the beating heart of this Leinster team. He is the barometer for their well-being.
When the talismanic second-row plays well, invariably Leinster play well, something Hines is fully aware of. And that is why the Wagga Wagga native attempted to distract the three-times Heineken Cup winning captain.
Hines' crack about his looks won't have cost Cullen a moment's thought. In fact, it's doubtful the joke Hines made is even known to Cullen. When it comes to Leinster and the Heineken Cup, Cullen is all business.
He will be more concerned with what he must do to ensure he and his second-row partner Damian Browne are the dominant duo in what promises to be a battle of attrition this afternoon.
Last week both line-outs had three throws pilfered. For a player as competitive as Cullen, that's three too many.
He will also have looked at the stats from both second-rows and seen that Hines made 11 tackles last week – Clermont's Jamie Cudmore made 13 – while Cullen's and Browne's returns were both in single digits.
That will annoy Cullen. He will want to dominate in every facet.
That is why the spirit of camaraderie that was fostered during the two years of Hines' stay in Dublin will mean nothing when the two teams battle over 80 minutes. From the first line-out, the first ruck, the first scrum, it will be about winning, at all costs.
Cullen is in the final year of his contract and has intimated that it may well prove to be his last season in professional rugby. He is on record saying he will reassess his situation over Christmas and make a decision then.
He has suffered greatly with injuries in recent years and there is a limit to how much punishment a body can absorb and still perform at the highest level. He does not, however, look out of place at Heineken Cup level. He is a magnificent ambassador for Leinster.
That he refused to be drawn into a war of words with his friend is evidence of his single-minded focus ahead of these crucial back-to-back fixtures.
There is nothing more important to Cullen than winning. The humour of twitter is now past tense. It's time to play, it's time for battle, it's time for war.
It's time for players to do their talking on the pitch. And, anyway, has Hines looked in a mirror recently?