To unlock the Bump 'n Crush trophy in Super Weekend Mode, you will have to kill one of the brown dust bunny heads that drop down the screen by hitting them on the side.
As they come down the screen, you will have to move out of the way as being hit by them from above will kill you. As they fall past you, you will need to press
or
and bump into them from the side. When you do it for the first time, the trophy will unlock.