Well, from what fans have observed, Jungkook tends to use informal language and slang in his daily conversations, which can sometimes sound adorable and hilarious to his bandmates. For example, he might use exaggerated expressions or mimic other people's accents, making his friends crack up. It's kinda like when you're with your friends, and someone starts doing a funny impression of your mom or dad.
In one interview, the group was talking about their favorite foods, and Jungkook started going on about how much he loves ramen noodles. His friends, RM and Jin, couldn't help but tease him about his enthusiastic tone, saying he sounded like a commercial advertisement. It's lighthearted moments like these that make fans love the group even more.