Why does the international date line have a weird hammer shaped pooch at the equator? Shouldn’t it just be straight all the way down?
The international date line has bends and wiggles for the same reason that other time-zone lines have bends and wiggles: to accommodate the needs of countries that it would cross if it were drawn as a longitude line. The weird hammer shaped pooch accommodates Kiribati, a group of coral atolls formerly known as the Gilbert Islands.
Chava
Without checking a map, my guess would be that there are a group of islands that whose governing body/people want them to use the same time, just as other time zones are shifted to contain entire states/regions/countries/whatever.
Whoops, a bit slow on the keyboard 
Thanks for the answers.
For good dateline fun, head to the island of Taveuni in the Fiji island chain. The island straddles the date line and they have a marker designating the ‘exact’ spot. Jump right- “Look, I’m in tomorrow.” Jump left- “Look, I’m in today.” Hours of fun! (Actually about 7.2 seconds worth of fun, but memorable nontheless.)