If you love chocolate one day and hate it the next, you've done a complete 180. In this case, doing a complete 180 means completely changing your mind. But if you do a complete 360, you're right back where you started, so bring back the chocolate already!

These expressions come from geometry: a circle is 360 degrees, and halfway around a circle is 180. When you've done a complete 180, you're facing the opposite direction from where you began. The expression to do a complete 180 refers to changing directions. Here are some examples:

Later, in the hall between third and fourth periods, I saw Digger, and I know he saw me — because I watched him do a double take and then turn a complete 180. (Red Kayak)

(She) just straight-up rotated 180 degrees and started walking in the opposite direction! (Dear Martin)

To do a complete 360 is to spin all the way around, so if you're on a snowboard, ice skates, skateboard, or just doing the hokey pokey, go for it. Also, saying a complete 360 makes sense if you're talking about the circumference of a circle. Here is the expression used correctly:

As he tried to put on the brakes, she grabbed hold of his arm, and together they spun around 360 degrees. (Small Steps)

Seven degrees is something like one-fiftieth of 360 degrees, the full circumference of the Earth. (Cosmos)

Although incorrect, some people say complete 360 when they really mean complete 180. If you used to be one of them, don't fret! You can still turn this around. To do a complete 180 is to do an about-face.