1. Your friends will change. For those four years of college, I had the best friends a guy could ask for. We did everything together. I lived with my best friends, partied with my best friends, sat out hangovers with my best friends, and everything else in between. It's essentially like having a family when you live with your friends. In short, it was awesome.
Now, I see those people that I literally once would call my family only a couple of times a year. Once we graduated, everyone moved away. My friends reside all over the country from New York to Washington D.C. to Seattle. It's pretty tough going from seeing those people every waking minute to basically never seeing them.
Quite honestly, it's pretty lonely without them. When I come home from class, there's no one to joke around with or just watch a TV show with before bed. There's no one to go grocery shopping with. It's just not the same.
2. Hangovers get worse. During my freshman year of college, my hallmates (2nd Elliot at Mary Markley Hall - probably the drunkest hall in the history of dorms) and I drank pretty much Tuesday through Saturday, causing all sorts of ruckuses and having all sorts of fun. I could drink 12 beers on any given night and wake up and make it to an 8:30 class no problem. Those days are long gone. Nowadays if I go to the bar and drink 12 beers I have to fully plan on zero productivity the next day and I have to purchase at least 2 32 ounce Gatorades for the morning.
I also think the worse hangovers are a symptom of the first bullet-point on this list, friends. When I lived at BOX the Sunday hangover was a ritual. Everyone would stumble out of bed and meet in the BOX living room, where we would plop ourselves onto our beer-stained couches for about 12 hours of television and joke-telling that would make the hangover feel a little bit better. Those were some of the best times I ever had, and it was while I felt like absolute trash.
I don't have those friends around to sit around and joke with every Sunday anymore. Now it's pretty much just me and my hungover self sitting around feeling miserable. When your by yourself during a hangover, the depressing feeling induced by the hangover is increased tenfold.
3. It's much harder to meet girls. I in no way mean this to be disrespectful to girls, but in college girls just have very little inhibitions. Girls get drunk and make horrible decisions in college, making it much easier for guys at the bars.
In the post-grad world, (most) girls tire of the getting-hammered-at-the-bar-and-sloppily-making-out with guys scene. Instead, post-college girls want you to take them on dates and actually put in some effort and maybe even iron your shirt for a date.
Moving back home certainly doesn't help anything. The bars that I frequent in my hometown largely feature middle-aged married couples drinking wine who probably already had 401k's when I was born. Even when I do meet girls my age around my hometown, we most likely have nothing in common because those girls have never left home and are probably in community college. Don't get me wrong, there are girls to be met and the process is fun, but it's just not as easy as it once was.
4. You don't automatically feel like an adult after graduation. This has been the toughest lesson that I've learned. I guess I always thought that once I graduated college I would just feel like a dad or something and be completely settled down. That's just not the case. I've had too much to drink on plenty of occasions, made some dumb mistakes, and generally acted like an 18 year old my fair share of times in post-grad life. That's because, quite frankly, I'm not that much different from my 21 year old college self. Growing up simply doesn't happen overnight.
Being single in your mid-twenties can be a weird situation. You want to be settled down and maybe just have a lemonade and watch a movie on some Friday nights, but the ultimate goal is to have someone to be able to stay in with you on those nights, so you feel compelled to go out and meet new people. I guess when I was a little kid I always pictured myself being married and doing yard work and paying bills and being really content at age 24, but life doesn't always agree with the grand plans you've made for yourself.