Trouble at the office?

I have been working at my present job for about a year now, and I am mostly well liked here and whenever I come back from Vacation most of my coworkers greet me lovingly and tell me how great it is to have me back and how miserable work was without me. a couple of weeks ago this new girl started working here and immediately started to flirt and tell me how cute she thought I was, Im not one to reject compliments so I said thanks everytime, I flirt in the office alot with many coworkers (its all in good fun) but I kind of stopped flirting with this girl, I kind of felt her getting a bit too close, anyway, a couple of days ago she went to HR and filed for ual Harrasment against me!! HR called me in and gave me my first and final warning, I could not believe it!!! now everyone wont talk to her and she complains about that!, and since all the other girls know about this they p by and mess with me about it, its funny in that way but Im still boiling that I have this on my record.