Driving under the influence is a crime that is never taken lightly. If you find yourself facing DUI charges and it is not your first offense, you will face much harsher penalties. Third offense DUI's are the most serious of driving under the influence offences. DUI basics Third offense DUI's are broken down into three tiers. These tiers are known as general impairment, high impairment, and highest impairment. There are several different factors that determine which tier your DUI is classified under.