News flash- it's illegal to park on sidewalks! And yes, you are parked. Leaving your buddy in the passenger seat while the car is still running and you run into the store, still qualifies as parked. Any time you shift into the "P" gear, you are parked, whether it's for twenty minutes or twenty seconds. Even if it wasn't considered parked- it's a freakin' sidewalk, cars do not belong there!
What if you hit somebody? Which one came close to doing to me the other day. I'd love to hear your defense when the police come- "geez, officer I honestly thought I was allowed to park on the sidewalk. I didn't expect there to be people walking there."
There's a whole parking lot there to use, just because you're only popping in to buy some booze, does not give you permission to do stupid things. And it is stupid. And thoughtless.