In Ranma ½, just consider how much time Soun and Genma spend together and just how much crap Soun puts up with from Genma. Of course it's all so their children can get married and carry on the tradition, sure it is.
They address each other as "Honey" and "Baby" in one episode for no real reason.
This doesn't even begin to mention the rather disturbing implications of the whole Gender Bender thing- of which only Ranma seems to be fully aware, and absolutely terrified of.
There is also the fact that Ranma's default "trick Ryoga" scenario is to dress up as a girl (well, more of a girl) and hit on him mercilessly, something that Ryoga is always falling for.
Including the extremely Fanservicey "waterproof soap" storyline, which has a huge number of furo scenes. At one point Ranma dresses up as an attendant and is briefly seen giving the mostly-naked Ryoga a back massage.
And the time when Happosai's curse robbed Ranma of all physical strength, Ryoga stepped in to protect him from the numerous enemies willing to take advantage of Ranma's weakened state.
In chapter 200, Gosunkugi tries to use a magical paper doll to get Akane to go an a date with him. However, the doll ended up on Ranma instead, and they actually went on a date (with Ranma in male form, even). This didn't happen in the anime, in which the doll ended up on Kuno, who misinterpreted it as a challenge to a duel.
There was a similar story where Ryoga tried to use a magical fishing pole to make Akane fall in love with him, but accidentally used it on Ranma instead.
In episode 87 when Ryoga falls on top of Ranma in the path of an oncoming train Ranma tries to get Ryoga off of him and all the movement makes it look like they're having sex. He also worries about Ryoga when he gets injured and carries him.
During the Herb Saga, while unconscious, Ranma was able to sense Ryoga dying, waking him up immediately.
On the Les Yay side of things, particularly in the early years of the fandom, many people tend to read a lot into Chinese Girl Shampoo's willingness to Glomp her Gender Benderreluctant husband when he is in female form, even if one (or both) of them are stark naked at the time. She's also perfectly willing to talk about kissing him, or even try to do it, when he's in female form. However, that canonically seems to be more Single-Target Sexuality; she makes it quite clear that she prefers Ranma's male form, among other things being quick to change Ranma back into male form before trying anything romantic on him. She's also insinuated that Akane Tendo is a lesbian and, in the same sentence, called her a pervert, and in one anime episode (the climax of the expanded Japanese Nanniichuan arc), outright tells Akane she wants to get Ranma cured because she wants a "real man" on her honeymoon.
Similarly, Nabiki Tendo calls Ranma "cute" on their first meeting (although she thinks Ranma is a normal boy at the time, and doesn't know he's a male-to-female Gender Bender currently in his other form), and when she notices the breasts, promptly prods and rubs them to confirm that, yes, they are real. When Soun regains consciousness, having fainted upon Nabiki indignantly telling him that Ranma is a girl, she proves her point by squeezing Ranma's breasts again. In a late manga story, she confirms that Ranma's breasts have grown larger by, you guessed it, squeezing them again. She also has a number of half-naked photos of Ranma-chan hidden in her room... although, admittedly, given that she takes and sells these against Ranma's will for money, it does make sense she'd hide them to prevent him finding and destroying them. In the anime, at one point when Ranma seems likely to get a cured, she asks if Akane really wants him to get cured, since it'd make their honeymoon so much more interesting.
Akane Tendo isn't exempt either, in the eyes of Fanon. Mainly due to how she is relieved when it appears Ranma is actually a girl... though that might have been because she considered an Arranged Marriage to be old-fashioned and a denial of her freedom, currently had a Precocious Crush on the local physician, and was constantly being attacked by the perverted jocks at school, who believed that she would go on a date with whoever beat her. This last fact even gave her a short-lived Catch Phrase of "I hate boys!", perhaps a Shout-Out to her fellow Rumiko TakahashiTsundere Shinobu of Urusei Yatsura, though the Catch Phrase disappeared well before Kodachi Kuno was introduced. Kasumi also tried to placate Akane to the idea of being engaged to Ranma by pointing out that Ranma was "half girl", while Nabiki once told Akane that she thought it was cool Ranma was a Gender Bender and, in the anime at least, mentioned that it would make their honeymoon "much more interesting" — something that saw Akane a little distracted.
The second movie also has a line where Ranma has to destroy a potential cure lest Akane get hit with it as well and Akane says to him "I like you just the way you are." Many have read much into that line.
In episode 87 after Ranma accidentally turns into a girl and learns that Akane is still gone she's shown looking upset and saying "Don't you know that without you I'm just..." (Akane sneezes interrupting her)
Early in the series Ranma has a Homoerotic Dream where he's male and naked in the bathtub and he's confronted by a equally naked Kuno in the bath who looks at him with a lovestruck gaze and tells him "I love you. I would date with you."