Parents of two- and three-year-olds find themselves most uncomfortable and embarrassed when their children have tantrums in public: in the grocery store, in the park, or—and this is the worst—in the (until then) silent sanctuary of the public library. Yet there's really no reason why it should be so embarrassing that your toddler is behaving like a two-year-old. Virtually every toddler has tantrums. So even if every head turns your way, and you think everybody is recognizing what a terrible parent you really are, just shrug your shoulders and say, "Two-year-olds."
The most difficult advice in the world for parents to follow is when they are told to ignore a public tantrum until it goes away. But tantrums shouldn't be treated any differently just because they occur in public. Don't reward, bribe, threaten, or punish your toddler. Don't get mad or start shouting back at your child. Just prevent any damage, encourage your child to quiet down, and wait until the tantrum plays itself out.
If you cannot possibly ignore it, scoop your toddler up firmly but gently and, with as little fuss as possible, take him outside, to the car, or to a bathroom. Make it clear to your child that he won't get what he wants by having a tantrum. Then either talk him down or just tell him that you'll both wait exactly where you are until he calms down. Don't be overly solicitous though. If you pay too much attention to your child in this situation, you are backhandedly rewarding him for his tantrum. Soon your toddler may start having a tantrum whenever he feels the need for attention.
Finally, try not to treat your child any differently in public in an attempt to avoid a tantrum. Don't go out of your way to avoid certain stores out of fear that your toddler will fly off the handle. And if you wouldn't give in to the same demand at home, don't give in to it in a store either. If you do, you can be sure that your child will notice the effect that your fear of tantrums is producing. In time, this discovery will lead to more deliberate and manipulative use of tantrums.
Take heart. This really is "just a stage" that almost all children go through. If you manage to handle tantrums well, your child will eventually grow out of them (at least as a regular event).