Most mangaka use humor to certain degrees. These come in many different forms from the extremely translator friendly forms to the one style of joke that every translator dreads, the pun.

Visual humor is the most translator-friendly form there is. If a character goes all chibi (tiny body and big head), grows cat-style ears, and does something cute, then there is no translation necessary. The visuals take care of it. Slapstick comedy is also visual and needs no translator help.

Hyper-dramatic humor only needs the translator to fit dialog to the images. If a normally mild-mannered character suddenly gets flame in his eyes, clenches his fist, and makes a profoundly over-the-top declaration, it's your duty as translator to make sure the English is as over-the-top as it is in Japanese. That's when you dust off words like "shall," or "must," and if you can fit it in, phrases like "rue the day."

Surprise-style humor is the type one sees quite a lot in School Rumble where a situation is built only to be turned on its ear when you turn the page. In these, the author is trying to set up an expectation which you as the translator must try to foster. For example in School Rumble Volume 2 on page 131, the author is trying to set up the expectation that the main character Tenma will recognize the male main character Harima. (Of course on the first panel of page 132, she mistakes him for something completely different.) The trick for the translator is to play the previous page straight, as if she did recognize Harima, without betraying the joke. Usually a translation with a light touch will accomplish this. Then go as over-the-top as necessary when the pay-off happens.

And then there's puns.

There have been puns in my translation career for which I've found and equivalent English word that has both meanings that the Japanese had. Every time I pat myself on the back so hard the red welts didn't heal for months. I was very proud of them. But most of the time a translator has only two options: joke substitution or choosing the meaning that moves the story along and abandoning humor. The decision is made a little tougher since most vocal hard-core fans want the second option in all cases.

When one meaning of the pun is a part of the thing that moves the story along, then going with the meaning that works for the plot is an option, but if the manga is written so that a joke is necessary in the spot and no similar word exists in English, then substituting a joke may be all that the translator can do.

As an example, also from School Rumble Volume 2 (page 43 for those keeping score), there is a point where Harima, egged on by his cousin, tries to confess his love for Tenma. The Japanese original uses the word kimi which means "you," but Tenma mistakes the word for a different kimi which means "yellow." The whole short scene is based on a pun, and if there is no equivalent pun, the scene will fall apart. I substituted a pun which played on the idea that saying "attractive you" would sound like "attractive view," and crossed my fingers that nobody would complain. (I think I got away with it mostly because I can use the translator's notes section in the back of Del Rey books to explain it.)

Most jokes are as fun for the translator as they are for the reader. But puns are a translator's bane. Still, getting a pun right is usually a translator's greatest victory.