Based on how many other characters he’s yelled at over his time of playing Mario Kart Wii, I’m surprised he hates Baby Peach the most out of all of the characters he has hated.
Baby Peach is a source of childhood trauma to me actually. Back when I was really young and I was playing Mario Kart Wii, she was the biggest pain especially on 150cc. Still to this day even when I've moved on to Mario Kart 8 on the Switch, she somehow still is sometimes an issue.
7:25 I've done a bit of studying on this part. As the game's programming works, the blue shell doesn't target racers that have already finished the third lap. By the time the blue shell was already up to beef boss, who was in third when that happened, Donkey Kong, who was in second, crossed the finish line, and the blue shell had already locked itself on beef boss before Peach and Toad passed him.
7:20 Donkey Kong had a blue shell in 2nd place for whatever reason and threw it during the millisecond where Poof was in 3rd, causing the shell to fly backwards to get him.