I couldn’t throw him as far as I could spit him

As they say in the media world, lots to unpack here. I believe this is a mashup of “I wouldn’t trust (someone) as far as I could throw them” (indication of profound distrust) and “within spitting distance” (close proximity). I included the latter as the phrase indicates measurement or distance, so that is possibly where “spit” comes into play. “Throw up” might also have been in the speaker’s mind which led to “spit (up)”. Not sure. In any event, a big thanks to Bobby Workman for sending this one in, and indicating there are loads more from the mouths of his wife and her sister. Stay tuned, malaphor lovers.