For veganism, I can think of three possible issues with smoking cigarettes:
- The cigarettes might contain animal-derived ingredients.
- The cigarette manufacturer might test the cigarettes on animals.
- Smoking the cigarettes might harm nearby animals (e.g., pets) and humans.
So, assuming such cigarettes exist (no animal testing, no animal ingredients), it should be vegan to smoke cigarettes as long as the smoker doesn’t smoke near humans (unless they consent to passive smoking) and animals.
Do such cigarettes exist? It seems so. For example, this German PDF from 2015 (article) lists which manufacturers and brands were/weren’t vegan at that time.