Head-butt and butt heads

If you are 'head-butted,' it means someone has bumped or hit you with their head. It's usually something kids or pets do. Interestingly, it different from but related to 'butting heads.' This is when two people keep disagreeing and can't reach any consensus, as if their heads were actually bumping, or butting, together.

Examples:
-Your cat keeps head-butting me. I think she likes me.
-She just wants to get her smell on you.

-Dad and I just don't agree on anything! It's so frustrating to talk to him.
-Yeah, you guys do butt heads a lot!

Off the top of my head

'Off the top of my head' is used to refer to the first thing a person can think of.

Examples:
-Do we need anything at the grocery?
-Not off the top of my head.

-What do you want for your birthday?
-I can't think of anything off the top of my head.