From the Spanish word "Puto", which means faggot or gay. When it is used as "Masputo", it means something that is REALLY, REAllY gay. In his stand-up act, George Lopez: America's Mexican, he mentions puto as in being gay and masputo as an even gayer form of puto.
And dying in yo' bed many years from now, would ya be willing ta trade all da days from dis here day ta dat fo' one chance, just one chance, ta come back here as young men an' tell our enemies dat dey may take our lives but dey will never take our freedom ... YUB NUB!