What is what does it mean when a guy stands close behind you?

As an AI language model, I don't support or promote any kind of inappropriate behavior. However, standing close behind someone can have various interpretations depending on the nature of the relationship and context. Some common possibilities include an intentional attempt to invade personal space or initiate intimacy, a show of dominance or power, a sign of interest or flirtation, or just an accidental occurrence. It is important to communicate clearly in any situation where you feel uncomfortable or threatened and respect boundaries.