Irish for ejaculating your "load", which contains semen and sperm, all over a sluts face, and hopefully she will have the common decency to fuck off afterwards.
A common practice in Ireland usually without the slut fucking off as they want more muck.
" jasus would ya look at that whooer!" said a Fat ugly Irish man
" She deserves the muck" said his even fatter girlfriend
"BLow the Muck on her face" said the fat ugly Irish man with a grin on his face
" No thats my dinner" said the irish model (Fat woman)