Why Nami calls him Sanji-kun? Since both officially joined the crew (by this, I mean after Arlong Park), they use special suffix when talking to each other. In case of Sanji, this is not surprising as he does the same with every girl he meets (as far as I noticed).

Nami, on the other hand, rarely uses such suffixes, with Sanji being the only none she calls Sanji -kun.

Is there any canonical reason for this?
Kun (君【くん】?) is used by people of senior status addressing or referring to those of junior status, by anyone addressing or referring to male children or male teenagers, or among male friends. It can be used by males or females when addressing a male who they are emotionally attached to or have known for a long time.


My guess is she's just being playful.