My 21st was recently and i didn't do anything. Not because i have no friends, unfortunately it fell during the university holidays and all of my friends had gone home. I stayed in halls by myself because i don't really have a home to go to.
Most people have really special events or celebrate with their friends and family, whereas i spent the day alone and didn't get a single card or phone call, only Facebook messages. I felt like **** at the time, especially when people would ask what i did for my birthday. But you know what? It's only 1 day of the year. There are bigger things to get worked up about.