Mine is a tortured derivation first from a quote from the scientist who (as best I recall from high school biology) invented the microscope. First thing he looked at was some standing water and dubbed all the microscopic creatures he saw "cavorting beasties." I don't know why but that expression stuck with me.
The 2nd component is my college affiliation (Georgia Tech - the Yellow Jackets) and hence the change af beastie to Beestie.
Dumb, yes. But I hate thinking up nicknames while staring at registration forms
