hello!! in am more general way, I tend to say the most flirty shit to them accidentally, which can fluster anyone caught off guard.
for example: "hey could you pass me the salt?" "sure! anything for the most beautiful person in the world" (dumb scenario but it's situations like this)

though I must say that there are more specific things I can do that can leave certain f/os very flustered. for instance, I can get honami really flustered whenever I lick my lip to, say, tase a remnant of food that stayed behind. or by me carefully bandaging and taking care of her wrists when she sprains them from practicing too much (because of lots of small, soft touches kshskb)

alternatively, there are f/os who seem so immune to getting flustered that they fluster me in return. talking a bit about kaede here, because who knows what can make her lose her cool ktbsksbs

thanks for the question!! this was an interesting mental exercise