This is done in Episode 1 "Ice Station Santa". What you have to do: As soon as you can go to Stinky's, go there (that's after you get the instructions on finding the four action figurines).
Then talk to the bug of Episode 1 of Sam & Max, who is on the dining table left of Sybil and Lincoln. Talk everything possible, and when things repeat themselves, stop talking. Then, engage another conversation with him, and there will come the animation with the Mexican and you'll get the achievement. ;)