A semtex grenade is the fat ugly heffer who will not let go.
The night after the grenade has been jumped by the unfortunate, it may develop into the semtex grenade (a sticky explosive made notorious by modern warfare 2) where the said grenade will not desist in contacting the grenade jumper via social networking sites or by phone.
The main objective of the semtex grenade is to bombard the grenade jumper with these texts, phonecalls and emails, into furthering the meaningless one night stand towards a more meaningful relationship.
:'Dude, heard you got with a grenade the other night, hard luck.'
:'Even worse. Turns out she's a semtex grenade, can't get rid of her.'
Refers to the result of the process by which a grenade, or ugly friend of a girl you or another wants to hook up with, develops in into a full force semtex grenade,as made popular by the Modern Warfare video game series, after someone agrees to jump on the grenade.
The grenade, mistakenly emboldened by your making "small talk" with her so that your friend can run game on her dime piece friend, begins to think that she is in fact attractive as well. Now in full force, the semtex grenade begins pursuing you, desperately trying to hook up with you.
"Yo, did you hear Mike jumped on that grenade for Tim last night. She's a complete semtex grenade, been blowing up his phone all day."
"Dude, that sucks. I hope he's rocking Flak Jacket Bro."