If pigs can fly, then I am Napoleon.

One of the easiest things that you can do is argue on a false premise; if a hypothesis is false, then its conclusion can be whatever you wish. This explains my title.

For a more concrete example, consider the following hypothesis: "$\infty$ is a number." It is clearly false, but assume that you think that it is true. Then $1+\infty=\infty$, which implies that $1=0$ (after subtracting $\infty$ from both sides). Therefore, we have shown that $1=0$, which in turn implies that any two numbers $x$ and $y$ are the same (use the following map: $\left(y-x\right)\cdot1+x=x$, where it is assumed, without loss of generality, that $y\geqslant x$). In other words, if we allow $\infty$ to be a number, then only one number will exist, which is absurd.

Real debaters defend the veracity of their arguments with irrefutable truths of which, hopefully, the opposition is ignorant. Fake debaters futilely exchange unsubstantiated (at best) biases ad nauseam. When you argue, first make sure that your premises are actually true and not a whim.