What does it mean if a guy stares at your chest?

The other day, two of my guy friends stared at my chest. I wasn't wearing a revealing shirt, but I'd like to think my boobs are kinda big. I noticed them staring for a couple seconds, and they said they were trying to read my shirt. It was such a BS excuse because they've seen the shirt several times before and it has large print on it.

They kept staring after I told them what it said, and my female friend even commented on how intensely they were staring at my chest and how it was slightly creepy.

They just made it so obvious. What should I think of this?
What does it mean if a guy stares at your chest?
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