<human>: Summarize the given text in a few sentences.

So yesterday I went to the store to grab a 6 pack and a couple 2 litters. When I came in I checked the lines and saw they were empty so I didn't bother with a basket. I got my 6 pack then headed down the soda aisle, seeing they were out of 2 litters of coke, I opted for 4 of the 1.5 litter bottles. They were bulky and carrying them was a pain in the ass since i had to grab them with the tops of my fingers with the six pack under my arm, but still wasn't worried because the lines were a non issue. 

Well by the time i got out of the aisle with all supplies the only two registers open were both swamped. I cursed my luck but saw that one line was filled with people that had fewer items than the other, so I started heading towards it only to be beaten there by a group of 3 with a basket FULL of stuff. I'm now standing there obviously straining to keep the perfect balance of weight distribution so I don't drop anything, when the guy sees me and says "Man you should have gotten a cart!" To which I half chuckled then went stone faced as I watched them unload their cart. As it turns out, all three people each had their own shit they needed to pay for, so it took them about 10 minutes to separate and pay for their items.

Now if I was in the opposite situation and saw a guy behind me with only 5 items I would let him go ahead of me. I assumed this was a just a "social rule" that everyone knew how how to follow. So reddit, what other social rules did you assume everyone knew and saw completely disregarded?
<bot>: Asshole people cut me off in line with a basket full of shit when I had only 5 items and wouldn't let me go ahead. What social rules did you think everyone followed?