Reciprocated playful office banter is fine. It's childish but it's okay to be childish with someone who wants to be childish also. Unreciprocated playful office banter should not exist.

Teasing friends is fine and good, all fun and games, but I think it builds deeper and more meaningful relationships to build people up rather than tear them down (even in jest). I don't make friends with people who tease routinely (all in good fun), but that's my choice. I tolerate it from family, because, family.

By the way, most school bullying starts as unreciprocated teasing. Yeah, teasing is childish and I too think friendships are better without it. Maybe it means I take myself too seriously, but I prefer to compensate for others' weaknesses (especially colleagues and spouse) rather than point it out to have a good laugh about it.

And if you're a kid, you're not going to be the one who complains about it. You don't know words like introverted or strategies like "haha that's funny, let's change the subject", you're just going to grin and bear it. And then the teaser (in total innocence, not maliciously) is going to be like, "well he always grins when I do that"...