> Really? Doesn't something being explosive mean it's highly unstable and reactive?
Not particularly, no. Some certainly are, but others require a great deal of activation energy to detonate. Nitroglycerine (another explosive medication) is notoriously touchy. But C4 is only mildly flammable; you can heat up your meal by lighting a piece of C4 on fire then put the fire out by smashing it with a hammer; it won't detonate like that.