sticking the penis in the mouth while giggling. Originally and ideally, the male would tickle the girl so she starts to giggle, and then quickly sneaks his penis into her mouth.
Do not confuse with giggle sex, which is not actually sexual at all.
female: "hehehoogg...*gag*...wa aw o ooing!"
female: "What are you doing?"
male: "GIGGLE JOB!"