One of the most misused data structures is the humble map; hashmap, dictionary, hash table, etc.
It's a great data structure for quick storage and access of key value pairs. Unfortunately, because of its ease and availability, it becomes pervasive at jobs it has no business doing. The problem grows most visible in dynamically typed languages that make the map a first class citizen (Python, Ruby, Clojure, etc.), but it can creep up in any language.
As a PHP programmer… I strongly object.
Everything is a map!
My most loved and hated feature in PHP is associated arrays. I’ve seen an associated array that uses 16gb of memory before, it was as beautiful as it was horrifying.