To be ruined financially

I thought I was playing it safe, but I almost lost my shirt on that investment

Pensavo di andare sul sicuro con quell'investimento e invece ci ho quasi rimesso la camicia

It's a good thing my friend decided not to sue the big company, because he was wrong and he would have lost everything he owned, including the proverbial shirt on his back

Meno male che il mio amico ha deciso di non fare causa a quella grossa compagnia, perché aveva torto e avrebbe perso tutto quello che aveva, compresa la proverbiale camicia

This expression refers to a complete financial ruin, as to lose one's shirt means to lose one of the most necessary possession