just the way you celebrate your birth day with friends and well wisher rejoicing with you while you dress up one of your best attires etc,its never like that in Japan 
As pointed out on Naver, instead of simply dancing  and rejoicing with you, youth in japan  are splattering each other with various combinations of flour, mayonnaise, tea, ketchup, tomatoes, tofu, raw eggs, Coca-Cola, orange juice, birthday cake, habanero sauce and, um, even lube. Here are some birthday celebrations....P
When Japanese Birthdays Look Disgusting and Somewhat Frightening
When Japanese Birthdays Look Disgusting and Somewhat Frightening
When Japanese Birthdays Look Disgusting and Somewhat Frightening
When Japanese Birthdays Look Disgusting and Somewhat Frightening
When Japanese Birthdays Look Disgusting and Somewhat Frightening
When Japanese Birthdays Look Disgusting and Somewhat Frightening
When Japanese Birthdays Look Disgusting and Somewhat Frightening
When Japanese Birthdays Look Disgusting and Somewhat Frightening
When Japanese Birthdays Look Disgusting and Somewhat Frightening
For example, this birthday boy was covered in 500 grams of flour, 200 grams of mayo, 100 grams of ketchup, a teaspoon of yogurt, a can of beer, a package of tofu, and an egg. P
When Japanese Birthdays Look Disgusting and Somewhat Frightening
This one is worse: Margarine, wasabi, whole tomatoes, a large serving of Japanese beef stew, soybean flower, and katsuobushi (dried tuna flakes). Blergh. P
When Japanese Birthdays Look Disgusting and Somewhat Frightening
"This is repulsive," wrote one commenter on 2ch, Japan's largest bulletin board. "I don't even want to think of them as a Japanese person like me." Another added, "These people are completely nuts." 2ch commenters also wondered what the appeal of these birthday celebrations were. P
so for you as a non Japanese what do think about this....will you allow your friends to dec you with the types in the above pics?...........let's have your view