Verpennt is a colloquial German verb that means to oversleep or to miss something because you overslept. It's a more casual and expressive way to say "verschlafen."
In the song, the line "Termin wird verpennt" (appointment is overslept/missed) perfectly captures a laid-back, perhaps even reckless, attitude. It's an interesting word because it's not as formal as other options, giving insight into the song's tone and the artist's persona.
"OOPS! (I Did It Again)" is a brag track. Miksu / Macloud and T-Low repeat the hook "Oops, I did it again" like it's an accident, but everything they list right after (a new chain, the gang, the cash, landing at number one) is exactly the point. The title winks at doing something wrong on purpose and loving it.
The verse pulls the curtain back a little. Between the flexing there's PTSD, drugs, codeine, and weed used to get through being alone, plus a hard rule against trusting people. Fame comes with the same two-sidedness: love from fans, hate from the cops, and a missed appointment because of a Xanax haze. The song never resolves that tension. It just loops back into the chorus, because the loop is the joke.