How to apologize?

Expressing regret:

I’m really/very/awfully sorry!

My apologies!

I apologize for…

I owe you an apology.

Please forgive me for…

Please pardon my…

Please excuse my…

Providing explanation:

I wasn’t thinking!

I didn’t see you/that.

The glass slipped.

I’m just too preoccupied with…

I totally forgot…

It totally slipped my mind.

It’s an oversight.

It’s totally unintentional.

Promise of non-recurrence:

I’ll be more careful next time.

It won’t happen again.

This will not be repeated, I can assure you.