Good questions Grover!
I've had bootcamp students ask me, "Is it OK to hit on someone at work?" The phrase, "Don't shit where you eat," fits pretty well. Brandon is right when he says a true blue player has no "modes." I have the feeling that you're highly over-thinking the situation.
The idea of "just be yourself" is simple, but the truth is that almost everyone is STILL trying to figure out who they are. How is it possible to be yourself, when you don't know who you are? I'm still figuring this out myself, and trust me, it's quite mind boggling and gives me a headache if I focus on it like crazy.
So you have your "Work" mode, your "school" mode, and your "party" mode. Party mode works only at parties, work mode at work, and etc. To my experience, the issue is CONGRUENCE. Google dictionary defines congruence as, "the quality of agreeing; being suitable and appropriate." In essence, your actions need to agree with your environment. If you're at a club, is it appropriate to be flirty? Of course! If you're working at a cubicle and your hot co-worker comes to you asking about such and such, would raucous flirting with her be appropriate? No way! That's probably a sexual harassment charge...
It's not just congruence to environment, but congruence to yourself. Are you a flirty and playful type of guy? Then be flirty and playful. Are you the funny silly guy? Be the funny and silly guy. Point is, just feel comfortable in your own skin, and people will naturally sense an air of confidence about you. Congruence to self and environment is an absolute must. It is a part of identifying self-confidence.
Quick story for you: my good friend Brian N. - who I haven't seen in 10 years since HIGH SCHOOL now lives in California. We talk on Facebook and we agree to meet up. After spending a whole day together, all he can say is that I'm just much more confident and a blast to be around since just by talking and being next to me, he can tell I'm comfortable in my own skin. Back in high school, we sorta knew each other, but at times he would choose other friends over me because I was shy, scared to step out of my bounds, and overall had a lack of confidence. He said in his own words, "You just didn't feel like you belong wherever you went Ben." Now it's much different.
When it comes to the workplace - Keep work AT work. If you want to date one of your co-workers, get some balls and ask her out for something low-investment such as coffee or lunch. Don't sarge her at work, move her OUT of the work environment and into a seduction environment. Keep in mind the entire idea of being comfortable in your own skin, and give her a date experience that she'll never forget
Hope this helps you out Grover. Let me know how it goes!