Because 7 8 9.
Because 7 ate 9.
Venutian blinds.
Because 7 (eight) 9
Ten. 1 to screw in the lightbulb, and the other 9 to provide emotional support.
Like Crap or Feces (its the same) WHY Because its Ca=Ca (equal sign is a double bond)
Omega!! Note: surely it already exists but I thought of it independently and am proud of my terrible joke!