Pokemon will only not breed if the old guy says "The two Pokemon perfer to play with other Pokemon". If it says that, the Pokemon will never breed. Otherwise, they will breed. It will just take longer if what the old guy says isn't really good, even if it says The two don't llike each other, they'll still breed. It'll just take longer.
EDIT: How does Traunt work? Does it mAKE Slaking attack like...
Attack, skip, skip, attack, skip, skip, attack, etc...
or...
Attack, skip, attack, skip, attack, etc...