stopping a suicide is a violation of ones ownership of their own life and technically a NAP violation for those who care about that, but if you are reasonably certain they will not harbor ill will to you after an aggression then there is no particular reason not to do it
other examples of technically aggression would be to bust someones door down when you notice a fire in their kitchen to put it out while they are away, they will certainly thank you afterwards
yet another, some people look at sex as an aggression, if you initiate it without permission then the other party is very likely not okay with this and it is commonly known as rape, but if you get permission first then there is no one to complain