i was leaving class today (college) with a few of my friends.. we walk by this table set up selling candy and stuff and the girl behind it (HB9) says "hey guys" and i was the only one that looked at her and she looked directly at me... this was an opportunity for me to approach and talk but all i did was smile and kept walking... i wasnt even feeling anxiety or anything

how should i have approached the situation in case i see her again

If you are having problems with being spontanius when situations just come out off nowhere its probably because you arnt comfortable enough talking to people you dont know.

Do you ever have any trouble talking to someone you know, when you meet them randomly.. Probably not. Cause then you are comfortable and calm.. and you have no problem introducing a topic.

If I would have been there.. I probably would have negged her about being a terrible salesperson.
You: So whats so special about this candy?
Her: bla bla..
You: And people belive that. OMG.. you're so terrible at this.
Im gonna buy some now, but only because I feel sorry for you. (C&F)
Then transition to: Was this your goal growing up? Becoming a popsicledealer and choclate pimp?

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Vino, vedi, vici.
I drank some wine, I saw her, I conquered