After seeing him and learning who he was, Tiara had to understand. She followed him home from a distance and watched him work the fields and orchards. It was just… wild to her that her busty rival was this, admittedly, handsome stallion and had no problems with it. In fact, he seemed to revel in it and loved showing off.
That's when she heard about the cider. She investigated further when she could, sneakily bringing it up to Buck's friends and family about what it was and stuff. Again, she just had to know.
Eventually, Applebuck caught wind of what she was doing and confronted her. Instead of being mad or curious, he just teased and poked her about everything. Something about what he said infuriated her to no end, especially when he implied she was jealous of him and his looks.
Then, with a few more low shots about her status, Diamond Tiara had enough. She couldn't let Buck taunt her like that. She had to show him… show him up on his own terms, no matter how crazy it was.