“bad”

Of low quality.

A person or thing which is unpleasant, dishonorable, or unwanted tends to appear (or reappear), especially at inopportune times.

Upon failure, it is easier to blame the tools used rather than how they were employed.

Which, especially which of an open-ended set of possibilities.

Something that is representative of all such things in a group.

To make a mistake, to go wrong.