101 Possible Reasons

Honked at the parking entrance by a black Mercedes. 

Sounded like an angry honk (or was it?)

Why?

He wasn't paying attention. Followed too closely and was startled when I turned left

He was just a crabby person

Merc vs Bezza: he felt superior

He was in awe due to the beautiful driver

He is a blithering idiot 

Testing out his car horn (new car perhaps?)

Wanted to follow me inside the parking but could not, because he forgot this tag

There could in fact be 99-101 reasons why this angry middle aged male/ person acted that way.

No matter. My Monday will be fabulous regardless.