The absolute worst variation of a joke that could ever, in all existence and time, occur. Usually performed by a specific person, see retard, hairy for more details. If you succeedingly accomplish a sparrowhawk, also identified as a "SH," surrounding persons are free to completely silence, injure, or at greater extents permenantly damage/disable the Sparrowhawk-er. A sparrowhawk could possibly be compared to a dud, joke assasin, only multiplied to an extreme extent.
"Please, save yourself before you Sparrowhawk, as you regullarly do, before I take that stapler, which should surely save you if you proceed."