I find it pretty easy to convince the world exist. If you assume you yourself exist, and think, and if you assume the contrary, that the world out there doesn't exist, you should ask yourself what alcohol and drugs are.
Because if the world out there doesn't exist, these things shouldn't effect the way you think. If something is simulating the world for you, you have to assume every time you drink, that thing alters the way you think somehow, which means it can access your actual real brain, whatever it is.
Then that brain of yours, even if it's outside the world, must be so similar to all the other brains you see, which are effected similarly by those same substances.
Because if the world out there doesn't exist, these things shouldn't effect the way you think. If something is simulating the world for you, you have to assume every time you drink, that thing alters the way you think somehow, which means it can access your actual real brain, whatever it is.
Then that brain of yours, even if it's outside the world, must be so similar to all the other brains you see, which are effected similarly by those same substances.