the act of prematurely ejaculating, usually due to extreme lack of sex or the opportunity to fool around with someone way out of one's league... as in only lasting a millisecond. Athough this is usually rather embarrassing for the person who "millied", it should always be brought up by friends in as many conversations as possible as a reminder.
"hey man, how'd your date with that hottie go?" "eh, not good." "did you milli again?" "I CAME EARLY ONE TIME!! LET IT GO ALREADY!!"