Mythones is a slang term derived from the French word "mythomane," which refers to a pathological liar or someone who habitually invents stories.
In the context of this song, it's used as an imperative, "Mythones pas," meaning "Don't lie" or "Don't make up stories." It's a direct and informal way of telling someone to be truthful, reflecting the raw and unfiltered language often found in rap lyrics.
"Bouteille" ("Bottle") is Timal's celebration of a lifestyle built on money, style, and good times. The hook repeats through the whole song: he pours himself bottle after bottle, on weekdays and weekends alike, while everyone around him notices how good he looks doing it.
The verses fill in the picture. He talks about the car, the clothes, and the cash that come with success, using them as proof that he's made it. There's also a sharper side: a few lines call out people who talk a big game without the lifestyle to back it up, telling them plainly to stop pretending.
Overall, "Bouteille" is a bragging, good-times track: part celebration, part warning to anyone faking the same success.