How come these girls were staring at me at the mall?

I was eating with my friend (who's a girl) and these 2 girls a couple tables away kept looking at me. When I'd look at them they would look away. I saw them looking at me when they were leaving too. I checked myself in the mirror and didn't have anything on my face. I'm not going to lie, it made me self-conscious when they were looking at me. It made me feel like they were like ewww? Why do you think they kept looking at me?