You can't bring coffee or drinks of any kind into a cleanroom environment so bringing one during the interview says to me nothing because if you get the job you're still not bringing coffee into the cleanroom. You can drink it outside and you can vape and smoke and get a tattoo in between your ball sack or buttcheeks but none of that will ever be done in a cleanroom environment. "One" other thing you are not allowed to do in a cleanroom is wear hair spray or aromatic aerosols or perfumes or makeup or clothing that sheds, or play loud music or wear your headphones or wear baggy clothes or not shower or bring your shoes or spit, pee or poo. But you can do all those one things outside. There are rules for every job and the rules may prohibit you from doing things you would otherwise do. Like doctors don't drink coffee during a surgery right over the open cavity. I'm not sure if a doctor may be allowed coffee on a table nearby. I'm not a doctor, so I don't know. A car mechanic could probably be allowed to drink coffee or other drinks while working on a car. A stunt pilot cannot be driving coffee during flight. A racecar driver also cannot drink coffee from a coffee cup while driving during a race. They might be able to drink from a helmet straw. So in sort I don't care what you drink during an interview.