The best instructors I've had are the sort of people you're happy going out for a beer (or ten) with. In fact all my instructors have been like this, occasionally they have been late, but equally there are days I've phoned in with a stinking hangover to cancel
There have also been days when we've both been sat in the plane ready to go, and one of us will mention "fancy a beer", and that'd be it, headsets off, and down to the pub