Daggers in mens' smiles?

Of course people have daggers in their smiles! Everyone on one occasion or another has flashed this deadly smile at either a total stranger or even someone they love. I feel it's apart of human nature; we are definitely not perfect. In my life, I have seen plenty of daggers among my friends (or at least people who I thought were my friends) smiles. At my old school in MN, I had a friend named Brianna. She was very popular, pretty, and outgoing. I didn't mind being her shadow- I'm no good at being the center of attention- and I always knew that I was her number one best friend. One day we got a new girl in our class, Kaitie. Although I wasn't worried about her, Bri seemed quite fond of her, and asked her to hang out with us. Kaitie started hanging out with us more and we were like the Three Muskateers! So I thought... I eventually got pushed back to the third wheel in Bri's eyes. Kaitie and I were still close so she always told me what Bri really thought about me: how I'm mean, annoying, and she was only my friend because I followed her everywhere (which isn't true because she didn't like it when I wasn't around). Of course, at school, I had to pretend around Bri that I had never heard these things otherwise she would know what Kaitie was telling me. Bri still smiled at me, laughed at my jokes and complimented on my clothes. All I could ever think about was what she was really thinking. Was she telling the truth, or just lying to me? I eventually found new friends but every once in a while, Bri would come up to me and complain about Kaitie, then just pretend like she never said it. This is how I personally know there are daggers in men's, and more so in women's, smiles.