If he would've said something more polite rather than basically tell me to get lost, I wouldn't have responded aggressively. Obese people aren't disabled. They can't move because they ate so much that their knees gave up. I've got no problem with fat people but this was ridiculous. Claiming you have a right to use something reserved for people actually disabled isn't a right thing to do much less with a rude tone.
That's not how civilised interaction works. Just because someone is rude to you (in the most mild means possible), it doesn't mean you can respond with insults or swearing.
And by the by, you shouldn't judge anyone who uses a disabled toilet (and neither should he). There are numerous invisible physical disabilities that both of you could have.
Also, you're a guest to the country. You should be on best behaviour, if only for the reputation of your fellow Argentines and tourists.
This man is going to go home today and share how rude you were to him to all his friends and family. As well as the security guard who chucked you out, or any of the on-lookers.
You make it all the more likely that confrontations will happen between locals and tourists.
What you should have done was simply left, or even mumbled a 'sorry' and left.
