This can be done on or offline but is easier on....Choose the engineer class and go to one of the bridges with a control panel near them.....if it is broken use the fusion cutter to repair the control panel....then plant a detpack on the control panel and go hide....when someone is crossing the bridge(even your teammates)detonate the detpack and send them plummeting to the bottom...this will not count as your kill but is fun to do on unsuspecting teammates...enjoy!!!