Is it normal to share cigarettes?
Mostly.Normal for most people
Yes, people do share cigarettes, especially socially, though plenty of people prefer not to. It’s not the most hygienic habit, since passing one around can spread germs.
It’s a familiar social thing in some groups—someone runs out, someone offers one, and the cigarette goes around. Other people find sharing mouthpieces too personal, so it really depends on the crowd.
The main downside is that saliva and close contact can pass along germs, including cold and respiratory bugs. You’re completely within your rights to decline or ask for your own; no big explanation needed.