A proton walks into a bar, sits down and orders a drink. After finishing the drink, the bartender says, "Would you like another drink?".

The proton says, "No, thanks."

A few minutes later, the bartender approaches the proton again and says, "Are you sure you don't want another drink?"

To which the proton says, "I'm positive."

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Editor's note: Yeah, it's a dumb science joke. Sorry about that