Never place any object between yourself and the airbag, such as a coffee cup or clipboard. Those items would be propelled into your face in a crash. Once the bag deploys, the bag and gas used to inflate it often catch fire. To some, the powder odor is noxious, but before you complain, consider the deadly alternative. Airbags deploy in any impact.
Some cars have side bags designed to deploy in a side impact.
One thing I didn't know is that some seat belts have explosive devices in the retractor mechanism, to instantly tighten the belt during a crash. Automakers are also experimenting with airbags to cushion your knees. I'm now convinced there's practically no downside to having airbags. I've listened to crash victims praise them. I've seen video of real wrecks with and without airbags.