Okay this is how it's going to go, you read my post, you post tips for demomen only. Let's start.
The Deception 1. Equip the sticky grenade launcher.
2. Shoot the grenade somewhere obvious in a doorway where an enemy will probably walk through.
3. Run into a spot where you can stay undetected but still see the sticky grenade.
4. Wait until the enemy approaches the sticky grenade.
5. If the enemy notices the grenade and attempts to deactivate it then shoot them in the head.
6. If they do not notice the sticky grenade then blow up the sticky grenade and shoot a grenade in front of them.
The Bounce 1. Equip the grenade launcher.
2. Stand near an enemy entry way.
3. If you see an enemy incoming then run out and bounce a grenade off of the wall.
4. Repeat step 3 until the enemy is dead or reveal yourself and shower them with grenades.
Camping 1. Equip the sticky grenade launcher.
2. Shoot a sticky grenade preferably on a ceiling in an enemy hallway.
3. Camp where you can not be seen.
4. Wait until an enemy is in the vicinity and then detonate the grenade.
TIP: If you are under attack while camping, shower the room in grenades, specifically the enemy.
Breaking and Entering 1. Equip the sticky grenade launcher.
2. Find a sentry.
3. Shoot a sticky grenade at the sentry.
4. Detonate the grenade.
5. Repeat steps 3-4 until the sentry breaks.
6. Direct your team into the room.
7. Win the match.