Ok. Here's a little social philosophy for you. I always say "people choose to be offended." What do you think?

Ah an interesting question to be sure. I think that it is a little of category 1 and 2. For example: If you saw someone had a green and red flag, and it enraged you and offended you to the point you start arguing with random people on the property or harassing staff or the owner, Yes. Yes you are Choosing to be THAT offended. However it is also possible to view say, some frat ritual where they have an eat a live goldfish contest and it genuinely upsets you because they are eating live animals that's a little different. You could be offended by it, but you may just walk past them and not cause a confrontation. So To a degree you can be offended and not be able to help it, and you could also act way more offended than you actually are. There is one thing you can choose and control, and that is how you react to being offended.

Only you control if you are civil and say "Uhm thats rather offensive, could you please not do that?" and going out of control "You $$$$$$$$ ****! How dare you &&&&& and ##### like you are some kind of @@@@@ %%%%%!" And only the other person can choose how they will respond in kind.

So to summarize, I don't think its impossible to be offended without choosing to be, but how you act based on being offended I think is more important. What do you think?

That's the point I try to make, it's comforting to see someone get it like you do. Alot of people don't understand it at all :/

When do you think enough is enough?
Such as when you draw the line between someone asking for a favor and them just using you.
Or someone suggesting something of you and them taking over your life.

That's a very difficult to judge because its so broad. I don't think this going to be the same for everyone. But lets take a crack.
I would say it falls into a few parts. How much effort are they asking? how much are they expending? how often they are suggesting or asking? what they are asking for? If someone asks for a small favor, and they show a lot of effort or thought put into it and they are not asking often for something, Id say that person just wants a small favor. Now someone asking for lost of small favors with a lot of effort put into it, and doing it somewhat frequently that might be a tad over eager. If someone shows no effort but is asking lots of little or big favors, that person is likely to just be in it for free favors.
Now if someone is asking for a BIG favor that really depends on on their motivation and frequency.

Being an artist I used to get these a lot. Id get people saying things from "Wow your work is amazing its so great." to "Draw my character doing A at B."
Ultimately I'd say the method they employ and motivation are the best ways to judge. If they employ polite and civil methods that's a good indicator. People who use passive aggressive methods should be a warning because that imply's something about their motivations. "Wow, Id love to get some of your art but I don't have any money for it. It would have been nice to have had my Sona drawn for once..." What I read from this is an appeal to pity, passive aggressive motivations and perhaps a desire to obtain free art. Its used alot on artists and used to get free pity art.
The best way to tell if someone is suggesting something, or if someone is trying to control is how they behave. Are they upset by it and angered when you say "Thanks but I think I am going to do it my way." or are they just disappointed or shrug? Thats another good indicator. This is a very complicated question but did I answer it?