The double text refers to impatient boys or girls usually desparate for their crush's attention. When two texts are sent without one reply making he/she seem desparate. Quite common, but more rare forms have been witnessed: the triple text and even the quadruple text.
Kurt: Hey babe you alright? Xxxx
Kurt: Oooh givin me the silent treatment r we? :P xxx
The double text has been committed- NO REPLY
Kurt: what u up to bbe x
NO REPLY - triple text
Kurt: Mornin you, alrite today? X
Texts usually hours apart then increase to days apart as sender doesn't want to look desparate even though they are also note number of kisses declines.