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A guy will chase you if he finds you attractive and you give him signals that you feel the same way about him too.
If by "chasing" your referring to guys following you around like mad stalkers and never talk to you. Then I hate it when they do this. Rather than taking the easier option and just talking to you. They just over think it all and over complicate it for themselves, by doing stupid things like lurking around you, just stands next to you all the time pretending to look busy. 2 years later, when you've lost interest. That's when they come over to talk to you.1