Reducing or eliminating your intake of calcium and vitamin D will result in bone disorders. That in turn can cause additional health issues. Not something to be experimented with.
There are certian vitamin thats help increase bone density, if you stop consuming them it would weaken your bones. I think its calcium and B12? dont hold me to that)
Yes, you can but it will take a little time. No calcium rich foods and lots of carbonated drinks will accomplish that and more.
You should watch Battle of the Warriors it shows the whole thing in scenic view.
eat like crap and stay on the couch. Chances are you have a good start already.
I am just curious. This question came to me one day and thought I should ask it. Is it even possible to weaken your bones purposely?