There are so many examples of bad English being used in Japan, so its not normally something worth mentioning. Occasionally though you come across a case that is particularly funny or ironic, and those can be worth sharing.
To be fair I probably make similar mistakes when speaking Japanese, so I don't normally find mistakes when people speak funny (Except for the Japanese guy who was talking about "the big election", but always confused L and R). However lots of Japanese companies use English in advertising campaigns and you would kind of expect them to have someone check it first.
Last time I was here I worked for a company which on their website offered "professional transration services" which fits the ironic category. One I saw last week might beat it though, an advertisement for a talking electronic dictionary that helps people learn English. The picture in the ad of course had a speech bubble, and what was it saying? "Lets Listening!"
The best Ive come across so far this time was when I went to karaoke last night. Lots of the songs are western and of course have the words in English, though not always the words you would expect. For example missing a space turned "I want you to hold me at night" into "I want you to hold meat ..." and a slight confusion between "you" and "your" gave "I want you baby" a whole new meaning.