According to a leading daily, Salman Khan was very upset with Katrina's smooching scene with Shahrukh Khan in the film Jab Tak Hai Jaan. Reportedly, Sallu wasn't upset with Kat for kissing his rival SRK, instead he was upset over the fact that Katrina had hid the fact from him for a long time. After Salman discovered the hidden truth, he stopped speaking to the actress ever since then.
Hence, keeping in mind about Salman's reaction over her onscreen liplock, she has apparently decided not to do it again. Talking to the daily, Katrina Kaif had also said that there's been no talks about any kissing scene in Bang Bang. In fact, the rumours about all liplock scenes in the film is false.