Unless your opponent is setting it up good, lead left hooks shouldnt be too hard to avoid.

The number one way to defend against a left hook is to keep your right hand up. If your right hand isnt up our gonna get tagged especially if the dude can set things up at all.

Dont worry about slipping, worry about blocking, especially because your getting hit with it.

Other than that it sounds like dude has a tricky little left hook. You have to keep your right hand up when your up against people like that.