Dani isn't exactly dense, it's more like she builds these really thick walls that not only keep people at a distance, but are also equipped with self-defense mechanisms that automatically try to rationalize everything as the flow of the writing. They keep her safe.
It's funny how differently Jiho and Chunyoung reacted to Dani's "explanation" of Ruda's kiss.
Jiho gets straight to the point and asks Dani if she thinks Ruda likes her. He is the one who reaches out first. Dani being Dani, says "of course not" with a confident laugh. Jiho gives her an exasperated look but since he's familiar with Dani's habits and has been subject to this behaviour himself before, is ultimately smug (lol) and satisfied with her answer so he just treats her like usual.
With Chunyoung, Dani is the one who looks for him as he's out on the veranda, away from everyone. She's the one who reaches out because he's giving her the silent treatment. Similar to how she addressed it with Jiho, Dani cheerfully says Ruda kissing her cheek was nothing. Whereas Jiho is comforted that Dani is unfazed by it and doesn't even think of Ruda in a romantic light despite what happened, Chunyoung gets agitated by Dani's flippant attitude about it. In an impulsive moment of jealousy, he kisses Dani on the cheek where Ruda did.
But he shot himself in the foot by doing it. Chunyoung once told Dani he "liked" her because she had no interest in him so she swore to never have feelings for him. Now he suddenly kisses her on the cheek and says things that provoke her, like "so you feel nothing even if I do this?" It hurts Dani because it feels like he's toying with her feelings.