Everyone at the beach would get sunburns. Ozone is molecular oxygen, and blocks the majority of UV light. Without it we are toast.
Every internal combustion engine would stall. This means that every airplane taking off from a runway would likely crash to the ground, while planes in flight could glide for some time.
All pieces of untreated metal would instantly spot weld to each other. This is one of the more interesting side effects. The reason metals don't weld on contact is they are coated in a layer of oxidation. In vacuum conditions, metal welds without any intermediate liquid phase (Cold welding).
Every living cell would explode in a haze of hydrogen gas. Water is 88.8% oxygen; without it the hydrogen turns into gaseous state and expands in volume.Molecular weight of Water
The oceans would evaporate and bleed into space. As oxygen disappears from the oceans' water, the hydrogen component becomes an unbound free gas. Hydrogen gas, being the lightest, will rise to the upper troposphere and slowly bleed into space through Atmospheric escape.
Everything above ground would immediately go into free fall. As oxygen makes up about ~45% of the Earth's crust and mantle, there is suddenly a lot less "stuff" beneath your feet to hold everything up.