idioms

Hello, Massoud—and welcome to English Forums.

I've never heard that idiom. To 'trust one's legs' means that one is confident of escaping a situation, I suppose.

I think that is a wrong rendering of a persian expression into english language which is not common and right in english and means that sb 's arrival in a place brings luck or bad luck.

Mohseni from Iran

Anonymousmeans that sb 's arrival in a place brings luck or bad luck.

Thank you, Mohseni. Very interesting. How would you put that into an English sentence, then?

hahahaha, this is most likely to be, I think, a literal translation from Spanish: meter la pata... it is used to express that you do something wrong or out of place in a given situation... the guessing of Mister Micawber really made me laugh..

Mohseni, I think the English phrase is 'Put your foot in your mouth' or 'Make a fool of yourself'.
Dougall from about 17 different countries

Though after reading what you wrote about someones arrival meaning bad luck, often in English we say 'Speak of the Devil and he shall appear'. If someone suddenly appears after one of a group of people has said to yet others 'hey wheres Joe?' for example, and then Joe walks around the corner. Its usually meant with a humorous and friendly side to it, at least when I say it