SB 3.31.34

teṣv aśānteṣu mūḍheṣu
 khaṇḍitātmasv asādhuṣu
saṅgaṁ na kuryāc chocyeṣu
 yoṣit-krīḍā-mṛgeṣu ca
Synonyms: 
teṣu — with those; aśānteṣu — coarse; mūḍheṣu — fools; khaṇḍita-ātmasu — bereft of self-realization; asādhuṣu — wicked; saṅgam — association; na — not; kuryāt — one should make; śocyeṣu — pitiable; yoṣit — of women; krīḍā-mṛgeṣu — dancing dogs; ca — and.
Translation: 
One should not associate with a coarse fool who is bereft of the knowledge of self-realization and who is no more than a dancing dog in the hands of a woman.
Purport: 

The restriction of association with such foolish persons is especially meant for those who are in the line of advancement in Kṛṣṇa consciousness. Advancement in Kṛṣṇa consciousness involves developing the qualities of truthfulness, cleanliness, mercy, gravity, intelligence in spiritual knowledge, simplicity, material opulence, fame, forgiveness, and control of the mind and the senses. All these qualities are to be manifested with the progress of Kṛṣṇa consciousness, but if one associates with a śūdra, a foolish person who is like a dancing dog in the hands of a woman, then he cannot make any progress. Lord Caitanya has advised that any person who is engaged in Kṛṣṇa consciousness and who desires to pass beyond material nescience must not associate himself with women or with persons interested in material enjoyment. For a person seeking advancement in Kṛṣṇa consciousness, such association is more dangerous than suicide.