ненадёжный человек, на которого нельзя полагаться(a person who supports others only when it is easy and convenient to do so; a person who cannot be relied on in situations of hardship or difficulty: I thought Gene would always stick by me, but when I got into trouble, he turned out to be a fair-weather friend.Asaula)
рысь битая(someone who is intelligent, has good common sense, knows how to handle bad situations, and has the skills necessary to function where they live, usually the streets Alex_Odeychuk)