To be honest, Akino did plenty of indecent things to Ichiko, especially during the beach chapter and trying to bath together if she won, probably not a "girl bath" together in normal way because she bought an expensive water-resistant camera...
So, birds of a feather flock together... still +20yo and a highschooler... major gray area.
Aihara said "do more indecent things to sensei", not "will do indecent things to sensei", oh he knows what they're up to, just two tsundare doing tsundare things, move along...