Well I guess to fill in some holes I will explain a bit furthur, I said "unknown reason" earlier because I didn't want to be too specific.
1. When my direct supervisor had a heated argument with another team member months ago, I defended my supervisor, and after the meeting butterface made a comment directly at me saying "hey, next time don't side with management", I told her she should be grateful because the supervisor was the person that got her the job, she insisted on the fact she got hired because of her "20 years of experience", which was a lie cos she had maybe 5-6 years tops. Later she went to my department manager to say I didn't respect her experience, and I apologized to her for what I said and supposedly "we were good". After that, I cut off all small talks and any non-work related communication, due the the fact I didn't appreciate her style of going beyond her ranks to complain.
2. After that at some point, I got questioned about my time management by the direct supervisor regarding a job, I considered it a double standard, and complained about excessive cellphone usage by other members, which includes butterface. After that, cellphone usage declined but butterface started to look at me in a hateful manner, sometimes walking right past me without saying "Good Morning".
3. First day after I came back from a monthly business trip and made some serious OT, and said Good Morning to butterface, she never responded. I tried that for a couple of weeks, she responded maybe 3-4 times. After that, it became a nod. Then just completely ignoring. I didn't want to add fuel to the fire so I let her work out her own shit.
4. I was away on Thursday for medical reasons, I used my own vacation day, and apparently somebody thought it was the perfect opportunity to ambush me, and on Friday, I got called at the end of the day to a meeting with the department manager to discuss this allegation of harassment aka "staring".