cut someone's throat

1. cut one another's throats . Engage in destructive competition. For example, With their price war the two stores were cutting each other's throats . This usage gave rise, by 1880, to the idiom cutthroat competition , for vicious competitive practices.

2. Be the means of someone's ruin, as in Joe would cut her throat if she got in his way . One can also cut one's own throat , that is, spoil one's own chances, as in Alice cut her own throat by her repeated absences . This hyperbolic term alludes to actual murder (or suicide). [c. 1500]