That means really fragile. And if it's underlined twice, that means very, very, extremely.
Und doppelt
unterstrichen bedeutet sehr, sehr, extrem...
Do yourself a favor. Read this part that Koko underlined for me.
Tue dir den Gefallen, Lies, was Koko für mich
unterstrichen hat.
The guy underlined every reference to animals in the Bible.
Der Typ
unterstrich in dieser Bibel jede Passage zu Tieren.