The boat vend tactic of blocking is one where the user simply refuses to vote to end the map. This is only useful on servers that require a percentage of clients to vote positively to enable a map's end. In JCoopZ, the command is known as "vote end".
Boat vend was first introduced by Casey who used it as a method to troll players in Zombie's Deadzone. Voting to end the map is done by saying (in the chat) "vote end". When the end is found, many players will say "vote end" in the chat to allow the map to progress. Casey enacted the boat vend tactic by, instead, saying "boat vend" which was met with much distaste.