It literally means pineapples. But in Mexican slang, it means lies. Someone who tells lot of lies, is a piñero.
Ese periodista es bien piñero. No leas sus artículos, son puras piñas. / That journalist is a liar. Don’t read his articles, they are all lies.
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I hope you have learned something new, about the spanish that real Mexicans talk on their everyday life.
If you want to improve your Spanish, I also give tutoring lessons on skype using this page that host many teachers from all over the world, and while I don’t really do grammar, I can help with conversation and doubts about the language. Also, if you are interested in any language besides spanish, there are teachers and tutors for any language there.