The Hebrew language (you know, the one that was used to create the universe) has words that mean rest, play, relaxation, and pleasant activities, while it has no word for "fun" (the word kef is Arabic). A "fun" activity has no goal, as is implied in the colloquial expression, "just for the fun of it." In other words, the goal of the activity is within itself, and fun does not lead to or result in anything else.
This concept is alien to Judaism (you know, the religion that grew out of the language that was used to create the universe). Every human being is created with a mission in life. This mission is the ultimate goal toward which everything must in one way or another be directed. Seemingly mundane activities can become goal directed; we eat and sleep so that we can function, and we function in order to achieve our ultimate goal. Even relaxation and judicious enjoyable activities, if they contribute to sound health, can be considered goal directed if they enhance our functioning. However, fun as an activity in which people indulge just to "kill time" is proscribed (um... what does proscribed mean anyway?). Time is precious, and we must constructively utilize every moment of life.
Furthermore, since people conceptualize their self-worth in terms of their activities, doing things "just for the fun of it" may in fact harm their self-esteem.
Rabbi Abraham J. Twerski
Yikes! I better get busy with something!!!