What are some useful strategies for people who knee-jerk contradict any positive assertion you make?

Minimize your contact with this person.  You are wasting your time with them.  They very well could be doing this just to get you riled up.  So once you stop giving them the attention they want, they could change their stance and move their attns onto someone else.

As stated previously, minimize your time spent with this killjoy.  If that fails, attempt to state indisputable facts as much as possible, especially in the company of others.  This will force the offending party to either remain silent or be shown as an idiot for attempting to argue that today is Wednesday, that 2+2=4 and that Obama is the POTUS.

There is one person i am dealing with atm that is exacly like this and he lives in my living environment, it is an absolute pain living with these types of people, They disagree with everything you say on purpose Another thing: you can be super assertive, but if the other person has a higher emotional strength, with other words a stronger energy or soul, they will make you feel bad even though you win the assertion intellectually or strategically

You flip them.  This can be done a couple of different ways.  The most common way is just to take the opposite view and wait for them to contradict it.  This is usually too obvious though.  Another way would be to ask them about the weather and then heartily agree, no matter what they say. Now they are trapped because they can't disagree without minimizing their own statement. For extra fun, get a co-conspirator with you to play along. Then when it seems like they might be catching on, go the other direction and disagree with them about everything.  At some point possibly you'll have proven your point well enough that you can sit down and tell them what you've noticed and ask them to stop.

sounds like this person wants to have a certain relative "position" to yours.... in general.  and it then manifests itself at every opportunity.  a creative person is usually able to spin just about any situation such that they can put themselves in that "position" with you.  if there's some good reason to subject yourself to this kind of treatment (IMO there almost never is), then you need to figure out the role they want, and either give them what they want, or discuss the issue openly with them and make them aware of it, and tell them they need to make some compromises. most of the time, the best solution to this problem is just to not so easily grant them this easy "position" relative to you.  because they usually are an unhealthy person to be craving it.  usually you'd want to simply stop being around this person.  there's a lot of other people out there you could be investing time in.