How do you know?

This question comes indirectly from my mother. She's not a Spanish speaker and likes me to translate passing conversation for her when I can. After telling her that the two young men we had just eavesdropped on were from Spain, she asked me how I knew.

Which got me thinking: How can you tell the difference between different dialects? For me, I look for differences in pronunciation or vocabulary.

e.g. If he pronounces "y" as "j," he's probably from Spain.
or
If she says "cipote" instead of "chico," she's probably from Central America.

What are some other ones? (Not just Spanish, any language, I find the regional variations of language fascinating)