I get on the bus and am sitting quite happily in my seat until the last stop on campus. The bus is very full and some old (and likely legally blind) guy gets on. Like a decent human being, I give him my seat. What does he give me? Jack all! Not a thank you or even a smile. Last time I checked, being old and being courteous are not mutually exclusive.
...Which brings me to another transit rule: "If someone gives you their seat, whether or not you 'deserve' it, say thank you!"