Well, the thing about wasps is the venom... So I would say a bb is way worse than a wasp sting, but the pain from the venom is worse. If a wasp was to sting you and inject no venom, they wouldn't be that bad at all (Diabetic here - I get more pokes than a pincushion daily)
Comparing it to a wasp sting may not be the best way to alleviate peoples fears. No-one plays with wasps for fun. Compare it to being hit by a hale stone.