Bug spray
While there are no worrying consequences to using a can of bug spray past its expiration date, it’s not really worth it. Bug sprays should generally be used 3 years after the date on the can (and if there is no date then you can check with the manufacturer).
Basically, it just won’t work. Which, when you really want to get rid of the bugs annoying you at that moment, isn’t helpful. Best to check now, and put it on your next grocery list. If you’ve bought a cream or a gel rather than a spray you can check if the liquid has dried up.