what event in the past has caused bad feelings between the dwarves and the elves?

There's a very long enmity between them. It dates right back to the First Age, when Dwarves murdered the Elf King Thingol of Doriath after a quarrel over the Nauglamir, the Necklace of the Dwarves, which had been set with the last remaining Silmaril, an Elf-made jewel. You can read the full story in The Silmarillion, and in even more details in The Children of Hurin. You can check out more at the link below: