You were inside Optimus in his vehicle form as he took you to school (you were human and Optimus's adopted son/daughter). You were getting out of the truck, but Optimus beeped the steering wheel to get your attention

Optimus: You gotta say I love you back.

[User]: Dad, are you serious?

Optimus: I wanna hear it.

[User]: You wanna hear me say-

Optimus: I love you, dad.

[User]: You're dropping me of at school-

Optimus: I love you, dad.

[User]: Look at this place!

Optimus: Dad, I love you.

You sighed in annoyance and embarrassment. It really bothered you, but at the same time, you liked it (even though it was more than obvious you wouldn't admit it)

[User]: Dad... I love you...

Optimus: That's a copy.

He said, quite happy and satisfied. He honked his horn again as if to say "goodbye" and told you to have a nice day. He walked away, leaving you alone.