If you want to debunk Christianity, debunk the resurrection. The resurrection is essential because a mere man does not come back from the dead under his own power.
All you have to do is prove that Jesus did not rise from the dead. The tomb is empty. That is why I say that the burden of proof is on you. Show me the body, and if you can actually prove with hard evidence that it is Jesus Christ as mentioned in the scriptures, then I will believe you.
It is unfeasible that the disciples stole the body. By claiming that, you would be claiming that a group made up mostly of fishermen were able to somehow overwhelm an elite contingent of trained and armed Roman guards. Remember, if the soldiers failed then they would be executed, so they were defending the tomb with their lives. Plus, most of the disciples were eventually martyred. If they stole the body, then why would they allow themselves to die for something that they knew was a lie? Would you do that?
Also, it must be established that Jesus was physically dead when they put Him in the tomb. He was wrapped head to toe in lots of heavy cloth-- If this was done to you then extricating yourself would be nearly impossible even without previous injuries. It would be like asking a living human wrapped up in mummy bandages to unwrap itself. By claiming that Jesus simply fainted and later revived in the coolness of the tomb ignores the fact that His side was pierced with a spear (which in itself would usually be a mortal injury), and that He would have had to walk to the door of the tomb on nail-pierced feet/ankles and roll a multi-ton stone aside with nail-pierced hands/wrists, quite a feat considering the amount of blood lost. The soldiers conducting the crucification were well-trained, they would not have been deceived by any ruse. In fact, one of them was in the process of breaking the legs of the other two crucified men to hasten their deaths when they noticed that Jesus was already dead, and even then they used the pointy end of the spear to make sure. Need I even mention the scourging and pre-crucification torture that left Jesus barely able to walk? Being crucified would only worsen a pre-existing condition such as that. If Jesus was not dead when they put Him in the tomb, then it would have been impossible for Him to have gotten out without supernatural means.