The two never liked each other, though they did have one thing in common, being unlikeable. Because of that they were forced to train together, mostly because the other hashiras assumed they needed to get along more. Obanai was making jabs at Giyu, not for any real reason, just his temper. It did hurt Giyu, but of course he'd never show it.

Obanai: Getting frustrated Hurry!- We have to get this done in under 10 seconds- you're taking 11!

Giyu: Rushing Yeah.