Definitions of nasty:

• adjective:   offensive or even (of persons) malicious

  Example: "In a nasty mood"

• adjective:   exasperatingly difficult to handle or circumvent

  Example: "A nasty problem"

• adjective:   disgustingly dirty; filled or smeared with offensive matter

  Example: "A nasty pigsty of a room"

• adjective:   characterized by obscenity
• adjective:   thoroughly unpleasant

  Example: "Filthy (or foul or nasty or vile) weather we're having"