I think Kate was enjoying being pursued, and when she was looking over the gifts, was upset with herself over the loss of a man she cared about, but played a game with for too long.
I think Gabi MIGHT be snarky towards JJ to cover her own guilty conscience. She was going with JJ when she first became attracted to Chad, nearly had sex with him a couple times.
She did not know what happened in Florida, (neither did JJ) until long after he had returned. So, actually, she had emotionally cheated on him, fully aware, and nearly and willingly, physically cheated...although Chad halted that, FIRST. She has never admitted that to JJ, but used the reveal of Lani having sex with the drunken, out of it, JJ as an excuse. Thus she covers up her own mistake. And now, well, there JJ is, with the woman who Gabi blames for the breakup, even tho Gabi herself is to blame, and it grates her. LOL