Keldabe Kiss: a gentler form of the kov'nyn ("head strike") used to express affection to another person when one or both Mandalorian(s) are in full armor, done by touching or tapping the foreheads of their helmets together. The keldabe kiss in particular is used as a substitute for kissing (kissing on the mouth, cheek, etc) and is often used as a greeting between Mandalorians. Keldabe kisses can vary by length or strength, ranging from prolonged forehead (helmet) touches to quick violent headbutts. Keldabe kisses are most often done between loved ones, which includes friends, family members, and lovers.
She ABSOLUTELY teaches Jacen about it. Sabine doesnt do these often but she'll do it practically all the time for Jacen. Its very cute. She'll squat down until he can reach her head and he'll come in relatively fast for someone who's not wearing a helmet. Every time they connect one or both of them says "bonk!"
Pre-Battle of Lothal when the Ghost family was all together she didnt do it at all really. That doesnt mean no one ever did it to her, knowingly or unknowingly
Kanan knew what it was, and told Hera about it. Ezra kinda picked up that it was a Thing™️ but doesnt actually know anything about it. Zeb notices when it happens but doesnt give it much thought. Chopper actually gets the most of them and he has no clue
Whenever Sabine would sit on the floor or crouch next to Chopper, sometimes (usually if he made her laugh) she'd lean a little bit forward and bump her helmet on his dome.
One time Zeb picks Sabine up in a bear hug and ends up with the side of his head on the top of her helmet. Its not a keldabe kiss but thats the closest they ever got
One time Sabine was excited to see Ezra after a fight, one where they were worried he was hurt, and she did a not very gentle keldabe kiss to the side of his refurbished stormtrooper helmet when they were all taking turns hugging him. She gives him similar treatment when they finally reunite post-Battle of Lothal
When Hera would leave the cockpit for her sleep cycle and she left Sabine and Ezra in charge, she'd often give them a kiss goodnight. She'd kiss the top of Ezra's head before pressing her forehead to the top of Sabine's helmet (if she was wearing it. If not she got a kiss too). Its not technically a keldabe kiss, but the intention and general gesture are the same
The first time she "bonked" Kanan it was when they were disguised as stormtroopers. They were trying to hug in victory but all the armor got in the way. They ended up just grabbing the insides of each others elbows and quickly bumping their heads together. Which is in fact a keldabe kiss, Sabine just didnt know that Kanan knew what that was. They have a few more over the years. Once Sabine was sad/upset and sitting at the table, so Kanan talked to her and when he got up to leave he leaned down to press his forehead to hers for a moment. Neither of them were wearing a helmet, but Sabine knew what he was doing. Their last one was done after Kanan was blinded. She gave him a hard bump to his metal eye-covering. They both laughed.
She doesnt get many when she moves back to the Wren Stronghold. Before she left for the academy, her dad would do it all the time to her and Tristan and even Ursa. It wasnt always forehead to forehead, but there was a lot of helmet bumping initiated by him (forehead to top of helmet, side of helmet to side of helmet when hugging, etc). He was the only one to give her any for the first few months after she came back
Clan Wren likes to bump helmets with returning members (if both are suited up). She remembers when they finally let her back in on that. She teared up a little inside her helmet
Ursa has always been more distant when it came to giving physical affection (she is mostly okay with receiving it, if its in private) outside of pats on the back or shoulder. When Sabine returned she was very surprised to (eventually) get a hug from her. These days they really only bump heads as a greeting when they havent seen each other in a while
Her and Tristan never really do it. They've done it twice in their lives and both times it occurred on a battlefield