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.'