Most of my mistakes were/are trying to explain something in Japanese. Everyone went/goes away none the wiser.
Just 2 weeks ago I was showing a picture of an eel (and it isn't really the best cartoon eel) and I repeated told them it was a cricket. They didn't seem to want to believe me and I thought it was because the picture was a little misleading.
Last year I told my nursing school students "asthma" was a "brassband performance."
a brassband performance that causes shortness of breath, wheezing and can be life-threatening.