Who said "This is the part where I come in, isn't it?"?

This quote is attributed to Marty McFly.

This is the part where I come in, isn't it? - Marty McFly

"This is the part where I come in, isn't it?"

Marty McFly

"This is heavy."

"There's that word again, 'heavy.' Is there something wrong with the Earth's gravitational pull?"

"I'm your density. I mean, your destiny."

"You're my best friend, and I care about you, but don't ask me to do this."