Kribbeln im Bauch literally translates to "tingling in the stomach," but it's a common German idiom for having "butterflies in the stomach."
This phrase beautifully captures the feeling of excitement and nervousness, especially in the context of new love. The singer admits he never believed in this feeling, making it a central theme of his newfound emotional awakening.
ENKAY spends most of this song admitting he was the problem. He had a whole system for not falling for anyone: "Und mein Herz hab' ich auch immer sicher verstaut" (and I always kept my heart safely tucked away), and the moment something started to feel interesting, "dann schalt' ich es aus" (then I switch it off). That is a lot of engineering to avoid a crush. Then someone walks in, the system stops working, and he sounds almost relieved to lose: "So lang damit verbracht, Mauern zu bauen, doch ich geb' auf" (spent so long building walls, but I'm giving up).
The chorus is where the German gets fun, because it refuses to be serious. "Keine neun, du bist 'ne zehn" (not a nine, you're a ten) is the kind of line you would text someone at midnight, and "Spannung hunderttausend Volt" (a hundred thousand volts of tension) is a compliment borrowed from an electrical warning label. The best line is the quietest one: "Hast mich repariert mit 'nem einzigen Satz" (you fixed me with a single sentence). He never tells us what the sentence was.