If they don't have much damage and the dash attack doesn't send them far I usually go into the neutral A combo or any one of the tilts. If the dash attack sends them a bit more than i'd like for a tilt then I just short hop and f-air or b-air.
edit: and by the way, I don't want to make a thread on this because its considered spam, but I've decided I'm going to hang out a lot in the diddy forums and hopefully get better with him. I'm not considering switching mains, its just that diddy is a really fun character to play and I think I'm gonna learn more about diddy if I play him a lot and talk about him with all you diddy mains
so, for the time being, I hope I get to know some of you, and you get to know me as the lucario representative of the diddy forums I guess...lol
Oh, and those of you that are worried I might spread the good news to scrubs that diddy is really really good, don't worry. I won't tell a soul