If it's threatening you or otherwise posing some sort of danger, then it's a menace. Angry rabid dogs, smog clouds, and annoying little brothers are all probable menaces.
The word menace works as both a noun and a verb, but it wasn't used to describe threatening or bothersome people until 1936. Before then, common menaces probably included things like the plague, locusts, and roving bands of pirate ships. Today, a bad reputation can menace an otherwise promising career, weeds can menace your garden, and burglars are a menace to society.