Guy's Behavior

Why do guys stroke and pat their stomachs around us girls?

Hello! I've read a similar question to mine on here, and like them, I couldn't find much info online myself. Okay so, the last few times me and my guy friend have been hanging out he's been lifting up his shirt (just a little though), and stroking his stomach then, patting it. From what I have found online (like I said I couldn't find much on this topic), he has his legs spread out a little I guess. And when he notices I'm watching he stops but then continues shortly after. I don't know if this is a subconscious thing guys do when they are attracted to someone or if he just feels comfortable around me, or both. He did tell me the night we last were hanging out that he does have a thing for me (it's too complicated to explain why we're not going out yet), so it could be he's doing this coz he's attracted to me, or is it a thing guys just do? And I don't mean this to sound weird but whenever I see my brother and his friends hanging out I don't see them leaned back into the couch stroking/patting their abs together lol! So why do guys do this around girls?
Why do guys stroke and pat their stomachs around us girls?
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