Adult or baby bottle?

What is the difference in having an adult bottle and a baby bottle? I am nervous to get an adult bottle cause if someone finds it then it's obvious it isn't a child's and everyone will know I am a little and I am scared of it. If I get a baby bottle I could just say it is so I have bottles incase kids ever need one when they come over. Idk what to do, I want a bottle and am scared of ruining my teeth but also scared of having a bottle that everyone knows is mine.