When two people go in for a handshake and one person puts up knuckles and the other person goes for a standard handshake. A fucked up handshake or a fucked up attempt at one.
The boss went to shake my hand and I gave him knuckles on accident. What a knucklefuckle.
A car, usually an old American car (1930's-1970's) who seems determined to skin, slice, and slash the hands of every mechanic who touches it, regardless of their skill-level. Resistant to tools, penetrating oils, vice grips, and laws of physics. Any bolt that is in this car will STAY in this car, whether you want it there or not, and if you try to remove it, it WILL break off, and leave you requiring 15 stitches in the process.
Holy Hell.........that '49 Mercury just tore my whole hand open, and all I was trying to do was change her damn oil!! What a knucklebuster!!
when one's aggressive ass-wiping causes him or her to forcefully strike the chocolaty log within the toilet bowl.
i was taking a behemoth dump on my break before i looked at my phone and saw that i had only one minute 'til punch in time. i was wiping so aggressively/quickly that i, accidentally, knucklebumped a floater.