[i_like_black]

I think you should man up.

You made a mistake, own up to it. You got the post deleted, at least. Explain what happened to your supervisor or manager, and accept whatever reprimand comes your way. Show that you're willing to be a better person.

Learn your lesson - don't bad-mouth your employer. It doesn't matter how shitty and useless you feel your boss is, they still hired you, and bottom line, they're still paying you to be there. You want the money so you go to work. That means accepting that the environment and the staff may not always be as great as you had envisioned.

If you do get fired, then you know exactly why, and you're going to have to explain this to future employers. If you come out and are honest about what you did, then you may get to keep your job, and with hard work gain back what will likely become a valuable reference in the future.

And, seriously, using a work computer? That's. Just. Dumb.
I'm sorry this doesn't have a lot of sympathy. I genuinely feel that being honest and accepting the consequences is the best way to go. It shows maturity.