bonk 
(bŏngk)
(bŏngk)v. bonked, bonk·ing, bonks
v.tr.
1. To strike or cause to come into contact: She bonked her head going through the low doorway.
2. Chiefly British Vulgar Slang To have sexual intercourse with.
v.intr.
1. To collide against something: His head bonked against the wall as he fell.
2. To become suddenly and extremely fatigued, especially in an endurance sport such as bicycling.
3. Chiefly British Vulgar Slang To engage in sexual intercourse.
n.
1. A blow to the head.
2. A hollow thud.
3. A state of sudden and extreme fatigue often experienced when participating in endurance sports, especially bicycling.
4. Chiefly British Vulgar Slang An act of sexual intercourse.
[Imitative.]