SexyBack’s totally fed up with people begging him to help ex-squeeze BRITNEY SPEARS get her sanity back – which is why JUSTIN TIMBERLAKE totally exploded when a woman approached him as he exited his agent’s office and scolded: “Why won’t you help her out? I’ve read she’s still in love with you. Can’t you just try?” Furious, Justin lashed back: “Why does everyone keep telling me I have to take care of Britney?… Britney, Britney, Britney!…She’s an EX girlfriend! Doesn’t anyone get it? We’re NOT together anymore. I am soooo totally over her!” And off he stormed. Totally!