Okay for that, you kept falling for the same trap over and over. But you should not retreat from an unarmed Diddy. If he's running at you without an banana, in your case they are gonna perfect shield grab you when you attack, or they will spotdodge you into an attack or grab if you misread it. You have some options for this actually.
You can execute a well timed fsmash, so they have to perfect shield the aura. I suggest that you do a retreat stutter stepped fsmash (RSS) to give yourself some more breathing room. If i'm correct only MK is fast enough to PS Dash Grab Lucario's Fsmash.
You can also run up to them as well, do an empty hop. They'll try to perfect shield into a grab assuming you're going to fair them. If you don't then they'll try to spotdodge, when they do keep the hop empty until you see the spotdodge then immediately let out a dair.
and probably the best bet, you can spam bas at the charging Diddy to slow him down.
Just reconsider your options a bit more. If you keep doing the same thing, then try to realize it and work around that situation.
http://www.smashboards.com/showthread.php?t=237886 we're actually trying to discuss them as well. Since it depends on what you want to use as a punishing move. My favorite is hopping above opponents and dair them.