As kids, we always sang it like this (I'm a teenager now):

Down by the banks of the hanky panky
Where the bullfrogs jump from bank to banky
Singin' eep, opp, eep opp opp
Skittle, dittle kernel pop
I pledge allegience to the flag
Michael Jackson is a fag
Coca Cola has caffeine
Now we're drinking gasoline
Gasoline ran out of fuel
Now we're drinkin' mountain dew
Mountain dew fell off the mountain
Now we're drinkin' from the fountain
Finally the fountain broke
Now we're back to
Plain old...
COKE!

And on coke the one person who was next to slap would try to hit the other's hand, and the other could pull away. If they pulled away the person slapping is eliminated, and if their hand gets slapped they are eliminated.