FYI, the spanish word for what you ordered is "elote" (usually plural "elotes" when painted on the side of the cart).
I'm not a huge fan because I'm not into the mayo, but they will usually make things to your taste -- especially if you saw someone eating from the cob, you should be able to just tell them that's how you want it. I don't recall ever seeing it served the way you got it, but like I said, I don't buy it very often.
I love the fresh tropical fruit vendors -- there's usually
one stationed at Pratt and Clark in Rogers Park. I could swear I posted about a great tub of fruit I got from them recently, but I can't find the link here.
Things seem to have cooled off a bit, but a few years ago, the city was actively subverting street vendors like this, so if you like their products, support them, and spread the word to people that they are good.
Here's a page which hasn't been updated in many years with a lot of info. I'm hoping that the city realized that these vendors are not a threat.
When you say "try authentic Mexican food," are you talking about restaurants? There's a great bounty. EatChicago
indexed David Hammond's "Beyond the Burrito" series, so that's one place to start. Of course, there's an overload of great Mexican food here in Chicago, so it might help if you tell us more about where you are interested in going or what specific foods you would like.
You could also look over the
Great Neighborhood Restaurants for Mexican restaurants highly regarded by people here.
Joe G.
"Whatever may be wrong with the world, at least it has some good things to eat." -- Cowboy Jack Clement