If someone did this in a tournament setting, they would be in violation of a Game Rule Violation (specifically, 307.1.
A player who has priority may cast a sorcery card from his or her hand during a main phase of his or her turn when the stack is empty, and technically stack is not empty until all players have passed priority.) , and the remedy is to simply back up the game to the point where the infraction occured:
If the error was discovered within a time frame in which a player could reasonably be expected to notice the error
and the situation is simple enough to safely back up without too much disruption to the course of the game, the
judge may get permission from the Head Judge to back up the game to the point of the error. Each action taken is
undone until the game reaches the point immediately prior to the error. Cards incorrectly placed in hand are returned
to the location in the zone from which they were moved (if the identity of the incorrectly drawn card is not known to
all players, a random card is returned instead). Once the game is backed up, it continues from that point.
In a more casual setting, while there is no official rule (it is, of course, casual) this is usually the best course of action to take. The first sorcery the player played is the one you keep, the rest go back to his hand, any cards that changed zones as a result of the errant cards go back to where they came from, etcetera.
On the other hand, if players aren't paying attention, then too bad so sad. What I typically do in this scenario is I give 2 or 3 seconds to see if anyone responds. That's long enough for it to sink in. If someone is legitimately distracted (hey, I get texts from the wife a lot while I'm at magic, too!) -and- there's a high likelihood they're going to want to respond to it (I'm Doom Blading their fatty or something) I usually take a small effort to point it out to them. If it happened over, and over, and over again, I wouldn't continue to give that extra effort. I would simply give the standard couple seconds, look for a couple nods, and continue on.
For what it's worth, I've played hundreds of multiplayer games, and I've never had a player who chained their sorceries more than once. I (or another experienced player) just tells then 'When you play a spell, check for a response'. (Even though they don't have to check for a response for chaining instants, as they continue to have priority, it is good to pass priority between them to limit your opponents' options to counter you.)