Often Bellybutton lubing is perfomed in preperation for a sexual act for either men with very small penises or women with very large belly-buttons.
"This ho got a belly so big after she had 12 kids i don't even need to lubricate it"
"After many failed attempts at penatration due to sizing problems, they finally tried bellybutton lubing followed by buttonpunching. However, indulging in this act whilst taking Viagra proved to be unwise. Trying to explain to the Ambulance Crew why this man was attatched to her abdomen proved tricky"