The act of vaginal penetration whilst inebriated and unable to sustain a full erection.
A stubborn attempt at sexual intercourse whilst physically unable to satisfy either party due to an excessive amount of alcohol consumed. Specifically resulting in a less than fully erect penis being forced uncomfortably into the intended recipient, 'like a slug'.
'man, i was with this steaming chick last night but i was so drunk i ended up slugging her.'
'this guy the other night was slugging me for about an hour before i made him stop, it was so disappointing'
'i don't really know what happened, i think we had sex but its more likely that i just slugged her.'