hell on wheels

Extremely difficult, unpleasant, or aggressive. That woman is hell on wheels when she's angry, so don't let her into my office. I can already tell that this client is going to be hell on wheels to work for.

Tough, aggressive, wild, or mean, as in Watch out for the boss-he's hell on wheels this week. This expression originated with the building of the Union Pacific Railroad in the 1860s, when it denoted the last town on the line, which was carried on freight cars as the track was extended. The town consisted mainly of tents occupied by construction gangs, liquor dealers, gamblers, and other camp followers known for their rough and often vicious ways.

Tough, wild, mean. This expression dates from the mid-1800s, especially during the 1860s construction of the Union Pacific Railroad. As the track was extended into virtual wilderness, freight cars moving forward as track was laid transported a town. It consisted of tents occupied by the construction workers, liquor dealers, gamblers, prostitutes, and other camp followers of a rough and unsavory nature. Hence the town was called “hell on wheels.” Later the term was adapted for any individual or organization considered very aggressive, as in “On Monday mornings my boss is hell on wheels.” It also has been used admiringly, as in “Don’t underestimate her; she’s hell on wheels for getting things done.”