On Sql Server can you disable an account at the database level?
You can simply deny connect privileges to the specified database. This may be less disruptive than dropping the user (in case you want to give them access again later, you won't have to re-create the user, set up all the permissions again, etc.).

USE database2;
GO
DENY CONNECT TO account_name;


When connect is denied, if they try to establish a new session connected to this database, they will get:


  The database database2 is not accessible.


If they try to select from a table in the denied database, for example, they'll see:


  Msg 916, Level 14, State 1
  The server principal "account_name" is not able to access the database "database2" under the current security context.


To give them access again:

USE database2;
GO
GRANT CONNECT TO account_name;