Protests and demonstrations are nothing unusual in Mexico, and it seems that there is always something to protest about. When I was in Mexico City in 2014, massive demonstrations were held across the country protesting the disappearance and likely murder of 43 students from a rural teachers' college. The President's inept handling of the situation only heightened the anger, and aroused suspicions of government complicity.
President Peña Nieto announced a 14-20% increase in the price of gasoline effective in January, with another hike scheduled for February. The public is generally outraged by this increase which is referred to as the "gasolinazo". Peña Nieto, who was already suffering from dismal approval ratings, is now even more despised. (I'd say he's running a very close second to Donald Trump as the most hated man in Mexico). There were demonstrations throughout the country, and some incidents of looting and attacks on gas stations. (My friend Alejandro says that the criminal incidents were committed by government plants in an effort to discredit the protest movement.)
While I was in the tranquil city of Mérida, the only sign of protest I saw was a handful of people on the main plaza with placards denouncing the "gasolinazo". When I arrived in Mexico City, which is usually a hotbed of political demonstrations, some graffiti was the only evidence of protest which I saw.
Then yesterday, not too far from my apartment, I witnessed a demonstration. A group of perhaps a couple hundred protesters gathered on Durango Avenue. From the logos on the yellow tee shirts that they wore, they appeared to be from the city of Chalco, to the east of Mexico City, and were members of the PRD, a left of center political party. They were very noisy, but perfectly peaceful. I kept my distance (foreigners are not allowed to even give the appearance of being part of a political demonstration), but I certainly did not feel unsafe.