Thundertail is a mean-spirited boy guppy, and that is why people don't like to hang out with him. He's very cruel - if he sees a ball, he has to pop it; if he finds an electric guitar, he has to smash it; and if there's a pig costume around, you can be sure he'll have it ripped to shreds in no time.
Thundertail's anger and bad attitude are infectious, so he rarely encourages anyone to join in on his adventures. On the rare occasion he does, you can be sure he'll deliver some bad-natured slapstick humor along the way. He is hardly ever the subject of the continuing joke that repeats during the episodes.