Mild annoyance.

This is tough to describe. You know how cartoon violence can be funny because despite the victim never appears to be actually hurt in a meaningful way and is fine the next scene? I think ecchi works the same way. The best ecchi is when the girl has something happen to her that would in reality be horribly embarrassing or emotionally scarring but in the context of the story doesn't really seem seriously effected by it. Like how a movie like Animal House can play off serious sexual deviancy as a "prank" because the victims just sort of run and scream like they saw a spider.

In simpler terms, bad things happen but she's only bothered a little bit.