Every year, without a shadow of a doubt, Sam Winchester gave his brother, Dean, a book for his birthday. When they were younger and unaccustomed to the details concerning credit card fraud, and so a little tight on money (as their father wasn't exactly the pocket money-giving-type, Sam would have to borrow a library book. However, since his first paperboy job at age twelve, he has prided himself on buying a new book each year. Within the 364 days between Dean's birthdays, Sam would read several books (purely for pleasure) and choose his favourite, but also a book that he feels would appeal to Dean, to present to his brother.
Every year, without a shadow of a doubt, Dean Winchester would put up his 'manly' pretence when given his birthday book, and say things along the lines of 'I don't care about this cheesy crap' or 'I'd rather receive torture' or 'the day I read is the day a vamp ganks me'. At first, he was worried that he had upset his little Sammy, a crime he would punish by death, but since the books kept carrying on, year after year, Dean figured that it was a terrible joke, that Sam was spiting him and therefore, that he wasn't hurt.
Every year, without a shadow of a doubt, Sam would find his unconscious brother in the mornings following his birthday with a torch and the book hastily stuffed beneath his pillow or, if Dean was particularly tired, the book flat on his face with the pages stuck to him by drool. Sam would pretend that he was unaware of Dean's secret, but he continued finding books, and buying books, and giving them to Dean, and wondering if he had enjoyed them.
That was until Dean died; Hell broke their tradition.