@salima,
In general, if there is someone who debases you in anyway, there must always be some sort of recourse. And when I say recourse, I don't necessarily mean "revenge" or "withdrawal" by any means, just to outline the fact that for every negative instance, there has to be some sort of reaction in order to maintain equilibrium. Equilibrium is essential to our own personal lives and society in general and your reaction is important to restoring it in most cases.
The important part, however, is what your reaction will be. All I can say is that the reaction has to be dealt in such a way where it brings things back to equilibrium. No over-reactions or revenge should be taken, only a restoration to a standard level. Tying this is with philosophy, there are countless philosophers (Descartes, Plato, etc.) who outline the consequences of passivity. Passivity in the sense that what is active is good and what is not is bad and contains all of what it means to be negative. This has been a huge problem in areas such as woman's right for example, where prominent feminists (like Betty Freidan and Simone De Beauvoir) underlined the fact that because women are put in a position of subjectivity and attributed aspects such as passivity, they are perceived as the "weaker sex." But they aren't necessarily the weaker sex though, are they? It's a matter of perception and allowance that puts them in that position hypothetically speaking. That's why (in my opinion) women have such a hard time climbing the sexist ladder and achieving some level of equality. On this note, there are then interesting anecdotes which feminists extol, such as this gem; "women must try twice as hard to be considered half as good as a man." But on that note, take the important parts of the example, that if there is some person putting you down, you have to confront the person is some way or another to bring equilibrium into play. And in the case of feminists, though it's a severe uphill battle, little by little there is a climb towards equilibrium and it involves some sort of reaction and a defiance against passivity. If you understand that there is someone pulling you down, you are being put in a passive posture where they feel it is acceptable to do that to you. The problem is not only that they do that to you, but that you allow that to continue. In essence, you are as much at fault then they are because you let them do that. But also in the type of situations you describe, passivity is hurtful not only to you, but to the other person as well. When you allow another to attack against you, that person becomes ever so liable to their own faults in the process.
Key point, you are not a toilet? so don't take cr@p from nobody. But then, that's for life in general. You get pushed around, chances are you will either get used to it or over react and get into trouble. So don't let it happen to begin with? plain out call people out when it first happens or prepare to encounter that a lot more in your experiences. Make it known that you know what's going on. I am not one of those people who overly agrees with people who turn the other cheek, but then I do not possess the level of patience and wisdom that they possess in those regard.
On the level of the forum, I would full heartedly agree with Didymos when he says that you should report posts that you find offensive or violate rules. I would suppose this is a sub-form of social contract theory. Before you joined the forum, you had no obligations to philsophyforum or anything like that, you were free to romp and play in the fields of the intra-nets carefree. But when you signed onto the forum, you cut a deal in which for access to the threads and so on, you have to adhere to rules and regulations of the community, which involve forgoing issues like these to moderators. By all means, carry on the conversation with your adversary in an intellectual way. Heck, they may thank you for it later, but don't take it to the extreme? it never tends to end in a good way for either party.