>> confirmation and amplification <<
It is indeed a very rude Dutch word, as confirmed by an online multilingual glossary of street slang ("Lo Piazza: Dizionario di parolacce") at the first web site below: "...hijo de puta = Hurensohn = son of a bitch = klootzak = Arschloch = asshole..."
However, it also appears in a number of sites apparently dedicated to international soccer and online combat gaming (see the second site below, which is in Swedish. The meaning in this language may be less crude; perhaps an inquiry in the Swedish > English area would be worthwhile).
Lastly, just for drill, here's an analysis of "Klootzak" as a baby name, provided online by a group (at www.kabalarians.com/male/klootzak.htm) apparently unaware of the potential downside of the name in Belgium and/or the Netherlands...
"Your first name of "Klootzak" has given you creative ability, imagination along practical lines, and the patience to pay attention to detail for a while. Although you are attracted to technical, mechanical, scientific fields, you lack the patience to follow through with this interest. This name gives a certain amount of practicality to your thinking; but there is also a tendency to scatter your efforts for, although you want system and order and stability in your life, you are too apt to be distracted from the job you are doing and to become involved in spontaneous interests. You are good-natured, have a good sense of humour, and are fairly easy-going, making friends with those who enjoy a good time. A weakness of this name is a tendency to make promises which you have difficulty in keeping. You tend to be lavish in your tastes and to spend your money freely. You have a heart of gold and are always ready to give generously. Since your feelings are strong and you tend to be enthusiastic and boisterous, you burn up your energies quickly and indulge in quick-energy foods, sweets, and starches. This type of diet affects the functions of the liver, causing either suffering with gall stones, jaundice, or skin troubles.
"This brief analysis of the baby name "Klootzak" is not complete. There are many additional factors (nicknames, last name, names and initials in your business signature, and birthdate, etc.) to be considered, or that affect your personality and life. A personalized Name Report™ will give you a comprehensive description of your unique abilities, inner potential, strengths and weaknesses, compatibility in personal and business relationships, career aptitudes, health, and degree of happiness and success."
Local time: 03:01
Native speaker of: English
PRO pts in pair: 953