Nickname of the 501st Legion of Imperial Stormtroopers. In addition to a group in Star Wars lore, there is also a costuming group of the same name.
"The soldiers of Vader's Fist are widely known for their level of dedication and loyalty".
Instead of fingering, one takes the whole fist and RAMS it in to a girls starport.
Hot damn! Lauren nearly sucked my fist into her blackhole when I gave her the ol' Vader's Fist!