THE PLT SAID THAT HE APCHD THE 6000 FT RWY WITH 40 DEG OF FLAPS. THE ACFT BOUNCED TWICE DURING THE LANDING, THEN THE PLT INITIATED A FULL POWER GO-AROUND. THE PLT REPORTED THAT THE ACFT DID NOT CLIMB, BUT WAS 'WALLOWING' IN GROUND EFFECT. TO REDUCE THE DRAG, HE RETRACTED THE LANDING GEAR, BUT THE ACFT SETTLED ONTO THE RWY. AFTER THE ACCIDENT, THE WING FLAPS WERE FOUND IN THE FULLY RETRACTED POSITION. THE PLT BELIEVED THAT THE FLAPS WERE ACCIDENTLY RETRACTED WHEN THE PASSENGER'S KNEE CONTACTED THE FLAP SWITCH DURING THE 1ST BOUNCE. THE PASSENGER WAS APRX 6 FT 7 INCHES TALL & HAD DIFFICULTY SITTING COMFORTABLY IN THE ACFT. HE RECEIVED A BRUISE ON HIS LEFT KNEE IN A POSITION THAT CORRESPONDED TO THE LOCATION OF THE FLAP SW. THE PLT REPORTED THE WINDS WERE VARIABLE & THAT HE MAY HAVE ENCOUNTERED A GUST OR WIND SHEAR.