https://www.polygon.com/2018/7/19/17590840/fortnite-giant-emote-bug-glitch

Fortnite is a pretty stable game for something that adds new features, weapons and items on a regular basis. Everything tends to work as its supposed to, despite the breakneck pace of development. That makes the latest glitch even more noteworthy, especially since it’s both harmless and delightful.

Here’s what you have to do to find the bug: Jump into an All-Terrain Kart, begin an emote and then switch seats. The emote becomes huge. You can watch a more detailed video for how exactly to pull it off at the top of this post.