In the July 13 airing of KBS' 'Super Junior's Kiss the Radio', the Girls' Generation members talked about YoonA and her teasing. 

Sooyoung said, "YoonA jokes by calling Tiffany a pig and she jokes around with me in a way I can't explain. When I get in the car, she says, 'You're copying me again. Annoying.' I have no idea how to respond to something like that."

YoonA explained, "That's how I show my love. I do that to make you guys laugh."

Sooyoung admitted that it is part of YoonA's charm, saying, "It's cute."

With her face turning red from laughing while she explained how she showed her affection, YoonA added, "Oh what should I do? My face keeps turning red," making the members laugh.

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It looks like YoonA teases and jokes with her members the same way only close friends can make fun of each other!