If DPS is regularly pulling mobs, tunnel visioning 20 yards away, rogue tanking, etc. you can just let them. Likewise, if a pet is taunting, pulling, etc, rather than go out of your way, you can just let them. In these cases, what tends to happen is either:
- Nothing: Everything is fine, and the dungeon goes smoothly
- Healer Stress: The healer tries to heal the DPS, and prioritizes them over the tank (inexperienced healer)
- DPS dies: The DPS or pet dies, and that person either continues doing the same thing later, or learns from their experience
- Communication (optional): You can try to discuss things with the group. Often, (of course, this is totally just my opinion), if people are not playing their roles properly, they either feel that they know what they are doing, and you don’t, or they have no clue (often both). This option is generally not required. I will typically communicate if I see a healer prioritizing healing a life-tapping warlock over a tank with low health though.