Questions about Mexicans staring/whistling

First off, I'm not a hot babe. I'm a dude, who is 1/4 Guatemalan, talks country, and dresses casual. I've always noticed how Mexicans will stare at people, seems like even they do it somewhat to each other. There is a small Mexican store I go into a lot to buy food, the owners who most don't speak English know me pretty well but on weekends they are full of Mexicans.

Today I went in there and there was probably 30-40 of them in there. Many times they would whistle back and forth to each other and many of them would constantly stare. I would even stare back and we would literally stare at each other for 15-20 seconds before they went back to eating. I was getting a to go plate for supper although I"m usually in there for lunch when its pretty empty. This is in Louisiana, pretty much all looked like road crew guys, and I dress blue collar I guess you can say, myself. Not like I was in there with a nice suit flashing money or anything. Basically, what is the whistling all about, and is that just normal culture in Mexico to just stare at people?

Also, as I walked out there was about 10 of them lined up outside talking and smoking, I nodded at them and they all nodded back. Its not really a big deal I was just curious if anybody knew their culture and if that's the norm.