The meaning of his tattoos
Some of the earthers had tattoos that meant something, but more often they were just pictures they thought were cool with no special meaning whatsoever except to make the wearer look prettier or stronger. If they had meaning, it was personal or something they had taken from somewhere else and affixed to their body, as if you could just interchangeably graft a lineage and tradition on your skin. So when sometimes someone would ask Ronon what his tattoos meant, he would tell me them "Nothing" and walk away. He had told his team that the tattoos were symbols of his family and house. John and Rodney hadn't inquired further and Teyla was too circumspect to ask more; she, however, of all of them knew that the tattoos meant something greater. If any of his team had asked, he might have told them--and only them--the story of the generations of Dex that were encoded into his skin, of the battles won, the poems written, the fields sown, the lineages that had prospered and those that had died only to be reborn again. And he might have given them his mark as well.
His relationships with Tyre and the others
The earthers all seemed jumpy as ilena about any relationship beyond that of a man and a woman (and jumpy enough about that as well) so Ronon never bothered to tell them about the deeper bond between him and Tyre and Rakai and Ara. Apparently, the earthers used to have something like it with their Greeks but had long ago left the practice and now had bizarre rules about fighters in the same ranks not being involved with one another, though apparently some nations were less backwards about it than the USA. He didn't know why the earthers had chosen to deprive themselves of knowing that you could turn to your fellow soldiers for everything, that on the eve of battle you could remind yourselves why you lived and what you fought for and soothe your nerves in the willing bodies of your companions. When you loved those you fought with, it could only strengthen your resolve. It made any betrayal sharper but, looking at his new team, Ronon thought the trade off was worth it.
Why he backed off of dating Jennifer
With his typical arrogance, Rodney had assumed that the best man had won with Jennifer, but Ronon had not told him that he had backed off his pursuit of Jennifer because of the harai-debt he owed McKay. It never did to let McKay know you owed him one, but with his removal of Ronon's scars not to mention the many times he had saved his life with his scientific knowledge, Ronon was in his debt. He had done his best to repay it by keeping McKay safe but really there was no way to quantify the debt owed or paid, as there never was with those that were your bondmates. And if Jennifer was what McKay thought he wanted, then who was Ronon to stand in the way, as much of a hard time he'd given him in the process? Though he liked Jennifer all right, what he liked most was the renewal of that part of himself he thought had died with Melena. There were other women in the world who might evoke that; however, McKay was pretty much one-of-a-kind.
What he had done before he was soldier
The earthers had some pretty set notions about what warriors did. He'd met a few that seemed to defy those--Lorne with his painting in his downtime and Sergeant Yu who told him his country had a tradition of warrior-poets, but when he first came to Atlantis they seemed to value him as a fighter most. His years of running had made him discard most of his artistic talents. They weren't things that would help him evade or kill Wraith, and the softer emotions and longings he'd shut in a box in his heart to survive and buried them so deep he was no longer sure he could even access them. When he'd had time for more than the next meal and the next Wraith kill and avenging his people, he figured it wouldn't do him much good to reveal to a people who would not understand the art of Satedan culture and the fact that Ronon Dex had been known as one of the most promising painters of his generation and a halfway decent hand at epic destime poetry and the songs of battle. But when he found the painting of the battle of Xerat, he kept it in pride of place and looked at it sometimes to remind him of what had been.
The name of his city
It was enough for them to know he was from Sateda, but it wouldn't mean much for him to tell him he had been from Calas. They would not know of the sparkling towers of Calas' main center, renowned throughout Sateda for their artistry and utility. They would not know of the fields of glaif that surrounded the city like a yellow ocean at harvest time or of the story of the city's founding, when the tribal war stopped over the graves of two men from warring tribes who had pledged to each other and refused to fight. Teyla might have heard in her travels, but she had left him to his memories in peace. Ronon figured he might tell his children if he had any or pass the stories down to Torren to carry on when he and the last of the Satedans were gone.