wums is definitely on to something.
Not just ISTJs but STs in general tend to tease people they like. To the STs, it’s a sign of flirtation or endearment.
To the NFS, it’s annoying, hurtful or even bullying.
ENFPs tease too obviously but again, intuitive and sensors don’t always speak the same language and miscommunicate.
I just recently read two stories of that scenario with two ESTP males and two ENFP females.