A Funny Thing Happened on the Way to the Whole Foods

Okay so I lied. It didn't happen on the way to the Whole Foods, it happened AT the Whole Foods. But it happened, all the same.
I always feel like I have weird interactions with the checkout people. Today was no exception. So I do my shopping. It's a super hot day, by the way, so you'll have to imagine me all gross and sweaty-browed. Oh! And unable to move half of my face on account of a visit to the dentist this morning. 
I get to the checkout and the checkout guy starts making small talk (as they always do at Whole Foods... it kind of annoys me). It's not that I don't like friendliness, it's just sort of... creepy... when total strangers ask you what you plan to make for dinner based on the ingredients you've just purchased. It sometimes makes me feel compelled to purchase the most absurd list of ingredients I could possibly think of. But then I would have a giant sea bass, a gallon of maple syrup, and a bulk supply of feminine hygiene products on my hands. We talk about how hot it is and how the city of Houston makes it borderline impossible for people to get around on foot -- The sidewalks suck (where there are sidewalks at all), and there are huge stretches along sidewalk routes with zero shade. Smart for 95ยบ weather (and that's on a cool day.) But anyway, we're chatting and I start getting self conscious about the fact that there is a huge line of people forming behind me. But the checkout guy is really not moving very quickly and anytime I make a comment, he stops scanning my groceries and pays really close attention to what I'm saying. I guess out of politeness? At this point, it's important to note that I have brought my own bags to the store and I notice he isn't filling them. Before I know it, I've paid and everything and he starts to get out paper bags. Before he fully opens the first bag I cut him off by saying, "Oh, I brought my own" and he replies with an apologetic, "Ohhh, sorry. I noticed you had your own, I guess I just forgot." So to speed things along I help him bag my groceries, and when he puts the last item into the bag he sort of raises his hand in this weird, unexpected way. 
So I give him a high-five and say "good job."
I HIGH-FIVED THE CHECKOUT GUY AND TOLD HIM "GOOD JOB!" As if he were a little kid or something. He laughs, but it quickly becomes obvious to me that he had not raised his hand with the intention of high-fiving anyone. But it was too late, the damage had been done. In a desperate effort to be really casual about it, I add, "cool, have a nice day." I'm sure that un-weirded everything.