If you ever come across a person having a seizure, you don't stick anything in their mouths. Never, never, never. This is something that my daughter lives in fear of, that some helpful soul will come across her while she is defenseless and stuff a spoon in her mouth. Stuffing a pen in the mouth is equally Not the Right Thing to Do. If you don't believe me, believe the Epilepsy Foundation.
So, what should you do? It's easy, and you don't need to be particularly heroic:
Seizures generally don't last more than five minutes or so, but afterwards, the person who had the seizure will likely be tired and maybe a bit fuzzy. Ask them if they would like a chair, a drink, a bite to eat. Ask if they would like you to stay with them for a bit. At this point, they will be able to tell you what they need. Believe them when they say they're OK.
Now, isn't that easy?