Imitation of non-Muslims or sinful people is not permissible, and is known as tashabbuh (unlawful imitation).
The following fall under tashabbuh:
- Imitation in a distinguishing characteristic of non-Muslim group/s or sinful group/s, seeing which in an individual creates a suspicion that he/she belongs with them, is like them or commits the same acts as them. 
- Imitation in a religious practice/custom of non-Muslims. 
- Imitation in something done with the intention of copying them, even if it is not religious or exclusive to them. 
It does not include something non-religious that is in principle permissible and not regarded as a distinguishing characteristic of theirs (e.g. certain forms of dress, eating certain dishes, dining on chairs and tables, speaking different languages, using certain medications or tools, using certain modes of transport, etc.) when not practised with the intention of copying them. 
It should be kept in mind that the example of the Prophet (ṣallallāhu ‘alayhi wasallam) is superior in all matters. Even in matters that are not religious – like the manner of dress, sitting, eating, sleeping and so on – it is recommended as far as possible to copy the Prophet (ṣallallāhu ‘alayhi wasallam) with the intention of being more like him.