Before answering the question how to lose friends after college, let's ask first why one would want to lose friends in the first place. Not sure for you guys, but I like to keep my close friends and relationships as minimal as possible, because (1) I believe that one can have too many close friends, and (2) I would like to protect my freedom as much as I can - and that involves getting rid of needless commitments, and yes, unnecessary friendships.
On having too many close friends
If you have a lot of close friends whom you'd need to attend all at once (due to same reasons), then you will be forced to prioritize someone or some few people only. You definitely cannot attend to all of them, but how can you even call yourself their close friend if you can't even attend to them when they need you?
On protecting freedom
The more close friends you make, the more commitments you will have to keep, and ultimately the less time/freedom you will get for yourself. Remember that if you want freedom, then always get rid of needless possessions, relationships and commitments. And I say, "give me liberty or give me death."
Now, let's try to answer the question, "how to lose friends after college?"
1. Be an asshole and not return any of your friends' calls, messages, invites, and Facebook notifications since graduation 2 years ago.
2. Be an asshole and say you don't believe in Facebook when asked why you're not replying to the thread for your group's upcoming reunion trip.
3. Be an asshole and say you're SO busy with work. Hence, you cannot take even 5 minutes out of 2 years just to inform the group that you're busy.
4. Be a bigger asshole and let your girlfriend apologize to your friends for your being busy.
5. Have no other reason for not returning any of your friends' effort to connect with you than being busy with work. Because, hey, you are the only one who graduated and is now working. Everyone else is not busy and is just dilly dallying at the corner.
6. And lastly, have asshole friends who will readily lose you for such asshole acts.
You're lucky your #friends aren't like that, and they all just want to (1) hit you with a chair, slash your stomach open, slap you repeatedly, pull your hair out, strangle you, and more importantly (2) meet you soon, hug you, kiss you, share jokes with you, and continue being friends with you.
We miss you.
You missed this year's B trip.
It's so ironic you were the one who desperately wanted to push our very first B trip.
Your #friend, you ungrateful bastard,