When a young Chosen/Digidestined girl begins flirting with Ken, Wormmon becomes very jealous.
Ken and Daisuke/Davis have their moments, too.
When Ken asks to give him some time to think about joining them, Daisuke doesn't get it and acts like he's just been rejected.
It's worth noting that Ken already showed interest in Daisuke when he was the Kaiser (the English dub gives us the glorious line "Seeing you squirm is so delicious!"), that Daisuke claimed to have heard Ken's heart talking to him, that Ken only manages to defeat his fear of the Dark Ocean and send Demon there after he hears Daisuke's words of encouragement (with Hikari and Miyako lampshading the process), that they engage in so much Say My Name that there's a video on YouTube teaching about Japanese Honorifics using scenes of their relationship as examples...
One of the 'insulting' nicknames Ken once used on Davis? 'Pretty boy'.
Nothing about Miyako? The blatant, Utena-inspired flowery fantasies of Mimi, then there's her and Hikari...
Hell, there's even some who see Ho Yay between Takeru and Iori (who are 11 and 9, respectively). Then again, given the "synchronize our hearts" nature of Jogress evolution/DNA-Digivolution, I guess the Ho Yay was completely inevitable.
The very fact that Jogress Evolution only pairs same-gender kids (Daisuke-Ken, Miyako-Hikari, and Takeru-Iori).
What about TK (Takeru) and Ken? In one episode (the one where TK Takes A Level In Badass and rips Ken a new one), this troper sensed a bit of flirting in TK's words, and the fact that they make Ken so flustered.
Oikawa's entire motivation is his suspiciously obsessive friendship with Hiroki Hida.