A medios chiles

Chile (chili) is at the center of Chilango culture. Medios chiles (meth-yaws-CHEE-less) literally means "halved chilies." When a person is said to do something a medios chiles, it means that such person did not put her heart to it, did not show enthusiasm and did not make her best effort. In other words, the person performed half-ass.

Madre orgullosa: Mijo, estamos tan orgullosos de que hayas terminado la secundaria.
Pepito: Y eso que lo hice a medios chiles. Si me aplico, igual hasta le prepa termino.

Proud mother: My son, we're so proud of your graduating from junior high.
Pepito: And all was done half-ass. If I apply myself, perhaps I graduate from high school.