Unfortunately there's about as much misinformation on this thread as there is good information.
1. It is not against any USCG rule to have expired flares on your boat.
2. It is against USCG rules to NOT have current (unexpired) flares on your boat.
3. It is against the law to fire off flares unless there is a true emergency.
4. Most fire departments do not want your old flares.
Now for the fun part. You can get permission from the USCG to hold an event where boaters can bring their old flares and legally fire them off. To do this, contact your closest USCG office. They can email you the three-page form you use to request permission to hold the event. It takes about 7-10 days to get that approval back.
If you are going to host one of these events (I planned one last month sponsored by our yacht club and open to the public and members of other clubs) you should:
1. Notify all local law enforcement and fire departments of the date/time/location.
2. Notify the local USCG of the date/time/location.
3. Notify all local emergency dispatch centers.
4. Veryify with your insurance carrier that your liability insurance will cover you if there is an accident where someone gets hurt.
5. We requested the local fire dept have an ambulance stand by for the 1.5 hour demo "just in case."
6. I sent out a flyer to the local boat dealers and marine stores to advertise the demo day.
At our event 52 people showed up and fired off between 250-300 expired hand held lighted and smoke flares and aerial flares of various kinds. Of the aerial flares, most were the 12-gauge type, but two people brought the 25mm flares. It was interesting to note that the ONLY failures were some flares that had expiration dates in 1988.
Most of the people who were there said that was the first time they had ever fired off, or seen fired, any of the various types of flares.
Here are a few pics of our event...
12 gauge flare pistol
25mm flare pistol (These went MUCH higher and stayed up longer than the 12 gauge flares)
25mm flares
Hand Held Smoke Signal
Hand Held Lighted Flare
The event was a success by all measures. We likely will do this again in 3-4 years and will publicize it better and hope for a bigger turnout.
If you belong to a local boat club or yacht club you might consider hosting an event like this. It's a good PR event for your club.
Expired Flares 
