Like the title says, Doofenshmirtz is the place to go for dating advice and explanations. Sure he has not had a very good record with it so far, most of his dates resulting in some pretty nasty results: I.E. the one that kept stabbing him with a fork, but his history with women aside he can spout some pretty good advice at times. Just check out how he does in the episode "love at first byte".
After that you still might be able to argue that his advice is rather, um, completely off, and I'll give you that, but it isn't really his relationships/ advice on women that I want to point out here.
Ok so kids usually watch Phineas and Ferb for the cool animation and story lines, while their adult guardians, or just adults in general, watch it for the little hidden adult humor bits that are slipped in, but in general they still think of it as a kids show.
Well they're actually only half right.
If you examine the way Phineas and Ferb is done you begin to realize that only part of it is a kid geared show, mainly the part with the titular characters, and the parts concerning Perry and Doof are really geared toward a much older audience. They address issues that most adults/teens actually go through, rejection, loneliness, and the issue of cheating on a person you're in a relationship with and how that can hurt. (Perry and Doof are NOT gay in any way, shape, or form. They're basically drinking buddies) And this is also where those problems are explained, and usually given a remedy. I mean have you seen the Peter the Panda story arc? Just watch the episode "Lost in Danville", no seriously, watch it, it is hilarious. Doof finds out he's Peter the panda's "other" evil scientist, and his real nemesis cant fathom why he's not enough for peter. It's like a soap-opera, almost. Of course Doof gives some great relationship advice.
Which later cumulates to this...
(sorry couldn't upload the video)
Don't you just love Doof? He just makes the day better.