A jovial person whose very presence causes you a great deal of unhappiness, unbeknownst to them. It's as if they're stealing your happiness and using it for themselves.
Not to be confused with a bully
or an asshole
, a happiness thief is oblivious to the fact they're stealing your happiness. They come in many forms, such as a heavy set woman wearing tight, revealing clothing, a co-worker rejoicing you with boring tales about their family, a person with an annoying, soul-piercing laugh, someone that smells unpleasant, and so on.
"That lady was clearly unaware that just because you're wearing 'stretch pants' doesn't mean you have to stretch them out. What a happiness thief!"