Pretty sure this doesn't fit your situation, but I really really like not responding, so that the person needing the help figures it out on their own and just does it and never again asks for the same favor. Tough love or something.
goes more like:
Them (me): "Hey Jeff, sorry for the delay! I was super busy doing important crap, hope you figured it out? lol"
you: "You're off the hook. Job is already done. Thanks anyway. You know, I really learned how to do some of this not-as-important crap and feel confident in accomplishing it!"
Them (me): "go me!"
you: "You're kind of a dick though."
Them (me): "

"
and scene.