Before forming the whip finish spin the bobbin to take out the twist you have built up in tying the fly. You can pull a whip finish as tight as you like but if the thread is corded up when you trim it the thread will untwist and the whip finish become loose. Something to cement it after is also a good idea.
"Political correctness is a doctrine, fostered by a delusional, illogical
minority, and rabidly promoted by an unscrupulous mainstream media, which
holds forth the proposition that it is entirely possible to pick up a ****
by the clean end"