A barco (BAR-caw) is a ship. In Mexican slang barco is used as an adjective to refer to somebody, usually a teacher or a supervisor at work, who is not very demanding. Sometimes is also used as a noun to refer to such type of person. GPA-conscious students crowd the classrooms of barcos (to boost their GPA). A superlative for barco is transatlático, which literally means 'transatlantic' and is a reference to ships of a ñero size.
Estudiante: ¡Chale! Me la voy a pelar con la beca si no subo mi pinche promedio.
Amigote: Alivianate, carnal. El próximo semestre la metes con el Profesor Godínez. Ese güey es súper barco.
Student: Damn it! I'm not gonna get that scholarship if I don't raise my fucking GPA.
Friend: Easy, bro. Next semester you gotta enroll in Mr. Godinez's course. That dude has a very low bar.
Another type of 'barco' that you'll find in Mexico City are Xochimilco's chalupas. These little boats typically navigate around Xochimilco canals, while everybody on board gets shit-faced and visits the bizarre Isla de las Muñecas (Island of Dolls).