I have a severe case of the flu and walking pneumonia. I went to work specifically to spit in a hated coworker's coffee mug.
How did you feel after you spit in their mug?
I enjoyed it quite a bit. Actually, I'm really proud of myself for having the courage to do that.
What you've done here is a very disgusting thing, and you shouldn't be proud of yourself at all. You just knowingly transmitted a disease which is illegal, and at this point I really hope that you're able to consider apologizing to the co-worker for what you've done. It doesn't matter how much you dislike someone, this was a step too far.
I only made a minor contaminant so I won't get in trouble
Are you sure about that, I am sure that there is something that can be done about trying to spread the illnesses. You should not intentionally get other people sick.