Front Bummer is in relation to Front Bum which is known as the female vagina. It is a term used either when a female causes interruption or stress to a male's life,or also used if the female has had an unfortunate experience.
"boys.. the gf will not get off my case about having a baby man what do I do?"
"sorry bro thats a total front bummer"
"omy gosh I just had the worst day of my life, my boss told me to quit voicing my opinion there was no room for feminism at the office, it was a total front bummer!"