"Bad company" or disreputable group of friends. They are not up to any good. Similar to 酒肉朋友 (which are people that you only go eating and drinking with - not having any meaningful conversation or deep friendship). 酒肉朋友 is a smaller scope, while 狐朋狗友 is wider in scope, outside of just eating and drinking. But similar concept.

In China, at least in the past, pig and dog are deemed as unpleasant and degrading animals (how unfair, since dogs are so cute and pigs are... yummy?), so the basic meaning of this word, or idiom means some silly and bad friends (from the point of view of the speaker), similar examples would be 狐朋狗友(since foxes are sly, so the meaning might be a bit different, maybe less lame?). My point is do not pay too much attention to the word, pig or dog. 猪朋狗友mainly shows the attitude of the speaker, that s/he does not like those friends of yours. But now, this word is less acrimonious, sometimes we young people in China use it as a self-mockery, for examples, 周末净和我那些猪朋狗友混了， I spent the whole weekend fooling around with my silly fellows. F.Y.I. Since my answer is purely from my experience as a native speaker, so it might be a lot different from the explanation in dictionaries.

Having louts as friends.

猪朋狗友=Some friends that you could get together for fun easily, but they are not your real friends. They would not help you out when you really need help from them.

one's bad/disreputable company/fellows