If you watch the bonus feature that comes on the VHS of Doug's 1st Movie (yeah, VHS is lame, but it hasn't been released on DVD, let alone Blu-Ray), even Jim Jinkins says the number one most frequently asked question about Doug is, "When is Doug going to kiss Patty?" But he ducks out and refuses to answer the question. Considering Doug got a feature-length film, that would've been a great time for them to kiss, but they didn't, and as far as I know there haven't been any new Doug projects ever since.
So Doug and Patty never kissed? After that episode where they almost-almost-almost kissed, I have to say I'm still frustrated about this even after all these years.
And yes, I know there was a fantasy sequence where Patty kissed Doug on the cheek, but fantasy sequences don't count.