<human>: Tonight, a friend decided to take me and a few other friends out to dinner tonight at a nice local restaurant. We were seated right away, our servers were nice, and our dinner was served in a timely manner. The food, as usual at this place, was good and, when the $80 bill came, I offered to pay the tip. 

Liking the place and the servers (along with having some familial ties to the restaurant), I decided that I would give a $20 tip. Upon seeing this, my friend rushed to have me put away my 20 and insisted on paying the tip himself, saying that mine was simply "too much." When I pushed the issue, he said that the amount of the tip was to be dictated by the person who pays the bill, insisting that this was a "societal rule" that I couldn't break. 

In my annoyance, I wondered what other "societal rules" existed so that, if I run into a problem similar to this, I can make a point to somehow work around the rule or, if that is too difficult, ignore it all together.

Can you provide a brief rundown of the text in within 3 sentences?
<bot>: I try to tip $20 on a good $80 meal. Friend paying bill refuses it, saying that "person paying bill decides tip." I'm curious about other societal rules.