In Volume 16, apparently something happened previously in Volume 14 or 15, but I can't seem to find it (I scanned the WHOLE Volume 15 to find this. I don't wanna bother with Volume 14. Please just tell me). From here and here:
During winter break, Hayasaka is constantly pestered by Kaguya who talks about her kisses with Miyuki in excessive detail. Eventually, she becomes frustrated and desperate to know what a kiss actually feels like. At the time, she's 'hanging out' with Fujiwara at a mall in order to distract and prevent her from ruining Kaguya's date with Miyuki. Hayasaka asks Fujiwara how she feels about kissing and when the other girl admits she would like to be forced into a kiss by surprise, Hayasaka does exactly that.
The only thing I've found about this is when it's described in a flashback in Volume 16 Chapter 152:
Question: Is it just this? Or was there something in a previous chapter?
Update: As answer shows below it's Ch162, the start of the very next Volume 17.
