Derived from the word p'twankyho. Similar meaning, but usually said with more "oomph".
-something has just occured (or not, as the case may be)
1)the sound a photon torpedo makes coming out of the Enterprise
2)the sound an explosive turd makes when jettisoned out of one's stink-bay
Holy Balls, I just p'twanked a pound of corn-log into the toilet.