The Rambam continues to speak of others that lose their share of עולם הבא. They are known as מומר, מחטיאי הרבים, and פורש מדרכי צבור.
The מומר is one who violates either the entire Torah or one particular Mitzva with no shame. He does this in a brazen way and does this with the intention of making a mockery and angering those around him.
The מחטיאי הרבים, are those that cause others to sin. They incite people to violate the Torah by trying to convince them of the irrelevance of its laws. This applies even if we were speaking of a more trivial law like Shatnez, or a more serious violation such as idol worship. Either way, he is dangerous.
One who is פורש מדרכי ציבור is one who separates himself from the community. He may not even violate the Torah but does not observe the commandments together with them. If a public fast is declared, for example, he will not fast together with the rest of the community. This is considered serious enough to cause such a person to lose his share of the next world.