When one has an erection (he) tucks his hard manship between his legs not allowing her or him to see his erection. Upon checking for head erection he opens his legs allowing his hard erection to hit her square in the face. Thus you have the thumkin pumpkin
Yo bro gave my lady a thumpkin pumpkin last night and today she has a black eye!
When you stick your thumb in the bumm and the love hole and alternate in and out in and out in and out as fast as you can making a noise like "nenenenene"
Tole threw trash out of the car when I told her not to so I gave her a double thumpkin.