wouldn't touch it with a ten-foot pole

Avoid it at all costs; stay away from it. The image of keeping one’s distance by means of a long pole dates from the mid-eighteenth century. It was preceded by “not to be handled (touch it) with a pair of tongs,” which appeared in John Clarke’s Paroemiologia (1639) and was repeated by numerous others, including Dickens. In the nineteenth century barge pole was sometimes substituted for ten-foot pole. Barges pushed with poles are seldom seen now, so ten-foot pole is what has survived.