A fork of Rural Dictionary
Depending on the inflection of your voice, or the actual event described, the slang term "How Fun" maintains two polar opposite meanings. The object of conversation may have been or will be really fun. If there is a hint of sarcasm in the voice or if the event is known to be generally dull, such as: I stayed at home all day and did laundry, "How Fun" would mean "bummer" or "how boring".
I went to Paris and then London to shop. How Fun!
I cleaned the garbage cans today. How fun.