The 19-year-old singer admits the `X Factor` chief tries to keep her and fellow panellists L.A. Reid and Britney Spears in line during filming of the talent search contest, but she isn`t afraid to stand up to his bossiness. She said: "Simon`s great, but he nags on me so much that I don`t know if I can take it any longer. "I`m a brat. I`m annoying. But I give it back to him." While Demi has clashed with Simon, she has made a firm friend in L.A., who says they will be best friends forever (BFFs). He told `Access Hollywood`: "Britney is such a massive star that it`s slightly intimated. She`s really sweet, just really loving and charming, but she`s intimating because she`s such a big star. [Demi] is like my BBF for life. BFFL. She`s really too good to be so young." As a judge, Demi admits she is very honest and sometimes finds it hard because she knows her opinion will upset the hopefuls. She said: "It`s really hard for me to smile if they`re performing and they`re horrible. "I have to be super super honest and sometimes I feel bad about it." Meanwhile, Britney thinks she is "fair" to contestants and tries to be honest without shattering their dreams. She said: "I think I`m a fair judge. Sometimes it`s hard because I know what they`ve been through and being so young and [wanting to] achieving their dreams. "It`s such a subtle and delicate situation when they`re that young so you just have to use constructive criticism and be there for them and just show them support."