Derived from the expression Hedo Dave and Cutting Out Early. A Half-Day Dave is a person who is never late twice in the same day. This means that if the person arrives to work late, then in order to not be late twice in the same day he must leave early. Typically, a Half-Day Dave person will arrive sometime after 9:30am and leave work by 3:30pm at the very latest.
Note that the Half-Day Daveer need not necissarily be named Dave. It has been seen on numerous occasions that The Rod is actually better at arriving late and leaving early than even Dave himself!
Hey The Rod - I see you have your Karate uniform... I guess you will be pulling a Half-Day Dave again!!!