Japanese phrase
勝手に使ってごめんなさい。 kat te ni tsuka tte go me n na sa i
Meaning
Sorry for using it without asking.
When to use it
Apologizes for using something without permission. It sounds casual and sincere when admitting a small mistake to a friend or family member.
Example dialogue
その色鉛筆、使った？ so no iro en pitsu tsuka tta
Did you use that colored pencil?
うん、勝手に使ってごめんなさい。 u n kat te ni tsuka tte go me n na sa i
Yes, sorry for using it without asking.