Demoman Vs HWGuy:

1. Introduction
Big fat and heavy. A demo has the advantage over heavy weapons dudes.

2. Strategy
If they are using Assault Cannon, you can beat them. Just hide behind a corner, and pop out and hit them directly with grenades. This is easy to do since they will be standing still. And throw a normal gren while you are at it also. A SSG using HWGUY is more annoying than an Assault Cannon one. But they are still very slow, and normal tactics should kill them.