If someone's giving you a shitty handy...
  1. Stop them.
  2. Ask them if you can show them how you touch yourself.
  3. Let them watch for a second so that they get it.
  4. Put their hand over yours so they can get a feel for what you're doing.
  5. Switch so that their hand is now on your junk and your hand is on top of theirs, guiding them.
  6. Remove your hand once they get it. Ta-da! You are now receiving a 100% better handjob.