mon and Tallulah have already given you great advice, so I'll just second/third what they have said and reassure you - this is a very very normal stage of development, and it's very very exhausting for all parents!
The only thing I'd add is you mentioned that you don't see this behavior in your friend's same-age toddlers or in other toddlers when you're out and about. When it's your child who's freaking out in the check-out line at the store or anywhere public, it can make you feel extremely self-conscious. That sooo happened with me with my first child in particular. I'd gone from having no children and being very aware when someone was in the store next to me and their child was screaming their head off and I would be thinking "why the heck don't they DO something about that!". The first time my up-until-then-very-quiet toddler went ballistic while we were shopping I just felt like the whole world was listening and I wanted to crawl into a hole and pretend I didn't know him because nothing I tried settled him down. BUT - if you really do pay attention, really look around - you'll find other parents also struggling with toddlers who are not at all acting like angels - they're out there - parents usually simply don't notice them because we're focused on our own kids. The other factor is - not all kids go through the "terrible twos" at the same time, or even at two - I have a 9 year old who is still prone to those tantrums, but she was an angel at two.
Hang in there - and enjoy your ds! Those early years fly by too fast, even though it can seem like the days drag on forever when you're in the midst of them.
Best wishes,
polarbear
