1. Dog Owners Will Never Achieve Heaven

๐Ÿ“šMahabharata 17.3๐Ÿ“š
Indra said. โ€œThere is no place in Heaven for persons with dogs. Besides, the (deities called) Krodhavasas take away all the merits of such persons. all Reflecting on this, act, O king Yudhishthira the just. Do thou abandon this dog. There is no cruelty in this.โ€ย  (source)

2. Ancestral Offering Gets Ruined by the Sight of a Dog

๐Ÿ“šGautama Dharmsutra 15.24-25๐Ÿ“š
If (a funeral offering) is looked at by dogs, Caแน‡แธฤlas, or outcasts, it is blemished. Therefore he shall offer it in an enclosed (place).โ€ย ย (source)

๐Ÿ“šApastamba Dharmsutra 2.17.20๐Ÿ“š
Letting Dogs or unqualified people look at Ancestral offerings is condemned.โ€ย  (source)

3. Dogs Cannot Look at Brahmins While They Eat

๐Ÿ“šManusmriti 3.239๐Ÿ“š
The Candala, the pig, the cock, as also the dog, the unclean woman and the eunuch should not look at the Brahmanas while eating.โ€ย  (source)

4. Dogs Cannot Look at Someone Fasting

๐Ÿ“šShatapatha Brahmana๐Ÿ“š
And whilst not coming into contact with Shudras and remains of food; for this Gharma is he that shines yonder, and he is excellence, truth, and light; but woman, the Shudra, the dog, and the black bird (the crow), are untruth: he should not look at these, lest he should mingle excellence and sin, light and darkness, truth and untruth.โ€ย ย (source)

5. He Should Bath Himself if heโ€™s Touched by a Dog

๐Ÿ“šBaudhayana Dharmsutra 1.11.39๐Ÿ“š
He who has been touched by a dog shall bathe dressed in his clothes; Or he becomes pure by washing that spot (where he has been touched), by touching it with fire, by (afterwards) again washing it and his feet, and by sipping water.โ€ย  (source)

๐Ÿ“šApastamba Dharmsutra 1.15.16๐Ÿ“š
If a dog touches him, he should plunge into water with his clothes on; โ€œor he becomes pure after he has washed that spot, touched it with fire, washed that spot again, as well as his feet, and sipped water.โ€ย  (source)

6. Deities do not Eat the Offerings if There are Dogs in Sight

๐Ÿ“šMahabharata 13.127๐Ÿ“š
Dhaumya said, โ€˜Broken utensils, broken bedsteads, cocks and, dogs, as also such trees as have grown within the dwelling houses, are all inauspicious objects. In a broken utensil is Kali himself, while in a broken bedstead is loss of wealth. When a cock or a dog is in sight, the deities do not eat the offerings made to them. Under the roots of a tree scorpions and snakes undoubtedly find shelter. Hence, one should never plant a tree within oneโ€™s abode.โ€ย ย (source)