Glashaus literally translates to "glass house". It's an interesting word because it's part of a well-known German idiom, similar to the English saying "people who live in glass houses shouldn't throw stones."
In the song, the lyric "Du wirfst mit Steinen, selbst wenn du im Glashaus sitzt" (You throw stones, even when you sit in a glass house) uses this idiom to describe someone who is resilient and perhaps a bit reckless, willing to take risks even when vulnerable. It adds a layer of depth to the character being described, making it a memorable and thought-provoking word.
Montez's "K.O." is a powerful tribute to someone incredibly resilient and strong, likely a parent or mentor. He's singing about a person who's faced countless challenges, saying "In deinem Leben gab es keinen Lucky Punch" [In your life there was no lucky punch], meaning they've worked hard for everything. Yet, they never give up, always getting back up, even when life hits hard.
He admires their unwavering spirit, noting, "Du wirfst mit Steinen, selbst wenn du im Glashaus sitzt" [You throw stones even when you're in a glass house], which is a bold way to say they're not afraid to fight for what they believe in. The song emphasizes that this person taught him that "man kann nur gewinnen" [you can only win] by never throwing in the towel. Montez sees them as a true champion, declaring, "Du bist der Champion aller Klassen für mich" [You are the champion of all classes for me], because no matter what, "du gehst nie K.O." [you never get knocked out].