I came on a co-worker's chair
Why did you come on her chair?
I was turned on by her.
Just because a girl turns you on doesn't mean you can ejaculate on her property.  You should only masturbate in private and clean up appropriately afterwards.
She knew what I did was right. She has a slutty body.
A woman having an attractive body does not in any way give you the right to make sexual advances toward her.  If you are attracted to this person, you should ask her if she would be interested in a date.  When you both feel the spark, then and only then can you can become intimate.