Does smoking a vape pen be bad for your health?

Yes: First of all, you become addicted to nicotine, which isn't a good situation for anyone anyway, but also increases heart disease. While it is probably not as bad as combusted tobacco in terms of tars and causing cancer, we simply don't know what the propylene glycol, flavorings, additives, preservatives, colorings and anything else in the stuff does in either the short or long term.