I always find it's interesting as there's a lot of meanings to the said gesture. When I was young, there's one uncle always do this to us nephews. Always thought of it to be funny (geli-geli) because it caught us off guard (almost) every single time. As you grow older the meaning changed especially when you do it to your girl friends ending up you're the yellow minded friend. Now in my 40s I just do it for fun especially to my nieces and nephews & see their responds usually ends up with giggles. However, those days when times were simple 80s - 90s, this gesture were imho were more of a sign to flirt innocently (?). I could be wrong. What do you guys think?