I will now give examples of some animes that overdid this compared to its manga.
1 rosario vampire in the komik jepang it is teen at most parts at least, In the anime they put a pantie shot almost every 3minutes which can be really annoying and ruin the epicness of the scenes.
However the worst one of my daftar is girls bravo. This anime went beyond words of fan service. The komik jepang was about 15 plus and had few mandi, shower scenes.
In the anime there was about 3 bath scenes with nudity per episode making it was mature.
HOPE THIS HELPED THOSE WHO DO NOT UNDERSTAND THE TERM fan SERVICE.