I think you're the one who's not understanding this. Under libertarian philosophy you have a right to self-defense which includes situations where you are reasonably sure your life is in immediate danger. For example if somebody with a bomb strapped to themselves came to your location you would be able to argue that you had a reasonable expectation that the man with the bomb strapped to himself was an immediate threat to either yourself or your property. Thus if you took actions to defend yourself it's likely any court would agree with your action and also unlikely a court would agree with the potential bomber's heirs if they tried to bring a case against you.
In addition to that property rights would further make this issue no more worrisome then it is today. Yes you have a right to strap a bomb to yourself, walk around, and even detonate it so long as that detonation won't harm another or the property of another. Your right stops at your property line, once you enter another person's property you must either play by their rules or leave. Most people are not going to be OK with some random guy coming on to their property with a bomb strapped to themselves and thus a person doing so it's a "law-abiding citizen." As the property owner would have a reasonable expectation that they or their property was in immediate danger they could take actions necessary to defend either.
Again I'll urge you to read the material I linked to (it's freely available at the link I provided) as it will likely clear up many of the misconceptions about libertarianism you seem to have.