Same picture as above, zoomed and cropped.
GRAAAARR! Actually, he's just yawning here. I don't know if yawning is an aggressive signal in polar bears.
Look at those teeth! Sorry there's no scale bar in this picture, just remember that his skull is probably 70cm long or so. His gape here is probably about 50cm, more than sufficient to bite all the way around my waist. If he was being really scary he'd probably pull his lips back all around, showing the teeth at the front more clearly and exposing the canines and molars along the sides.
After sniffing at us for a few minutes, he wandered off in the general direction of the mom and cub we'd seen earlier. Polar bear males frequently kill cubs, especially when they're hungry (e.g. mid-summer). I don't know what happened after he left us, but mom and cub had a good 10 km head start on this guy, and he wasn't moving very fast, so I expect they're fine.