I think it is so named because it sneaks up on you and then gets you with a deadly sting.
Scorpion Bowl
[makes 6-8 cup 2-3 person bowl]
1 shot (1.5 oz) Dark Rum
1 shot (1.5 oz) Brandy
2 shots (3 oz) Light Rum
2 shots (3 oz) 151 Rum
2 shots (3 oz) Triple Sec
18 oz Guava Punch
2 oz Pink Grapefruit Juice
2 oz Papaya Juice
5 oz Orange Juice
mix with cracked ice
drink through big long straws
preferably served in a fun communal bowl, possibly coconut shells
Update: By the way, this is obviously more than a single drink-equivalent. It is strong, but it doesn't taste that strong. It is specifically designed to be drunk by more than one person- the restaurant wouldn't serve one to just one person. Use with extreme caution, don't drink and drive, drink responsibly. Etc. :)