SHORT TAKE:
Forgettable, crude and violent dark comedy about pill-form marijuana, drug lords, murder, kidnapping, adultery and boardroom betrayal.
WHO SHOULD SEE THIS:
Don't bother. Go watch What’s Up Doc? Instead.
LONG TAKE:
In the 1972 slap stick comedy What’s Up Doc? 
there is a suitcase full of fossils which gets mistaken for a similar bag full of diamonds, 
which looks like another bag full of top secret government papers, 
which is the same shape and brand of luggage that is full of underwear. 
The suitcase full of fossils is really not worth much to anyone except its owner. 
However, because it is mistaken by different people at different times for other bags which are more valuable it gets: switched, stolen, moved, thrown, kicked, hidden; endures having to go along for the ride during a kidnapping; suffers through a high speed car chase; is sequestered in: 
a messenger boy’s bike basket, 
a Chinese dragon, 
a Volkswagon; is dunked in the ocean; and 
dragged into court as an exhibit.
What’s Up Doc? is a VERY funny throwback to the old 1930's and ‘40's screwball comedies of Frank Capra, Billy Wilder and Howard Hawks. Now imagine if you WERE that suitcase, your perception of just how humorous this all was, would be quite different.
SOME SPOILERS
The premise of Gringo is that Harold, a nebbish shlimazel (a fearful timid, unlucky loser) played by David Oyelowo (Lincoln, Interstellar and The Cloverfield Paradox) is sent to Mexico to help negotiate a deal involving pill form medical marijuana in Mexico for the pharmaceutical company he works for. 
Little does he know that: his company is about to merge and he is expendable, his boss, 
Richard (Joel Edgerton – Star Wars as the young Uncle Owen, Red Sparrow, Bright) has sent him to deal with a Mexican drug lord because he is expendable, and his wife is leaving him FOR his boss so that in his marriage he is…expendable.
Things go pear-shaped very quickly when Harold finds these things out and he decides to fake his own kidnapping with the help of some low rent motel managers who think he is more valuable to his company than he is, 
ultimately triggering pursuit by a Mexican drug lord who mistakes him for the "boss," 
which results in the hiring of a reformed mercenary with a conscience who is given conflicting orders which, in turn, challenge his new found repentance. Harold, in case you missed the point, is the bag of fossils – a fitting analogy since he has stagnated in one place for a long time, only to be buried and ignored by the people to whom he is loyal. "Why is it I am always getting s*&^%ed for doing my job!" Harold wails.
This movie,
directed by Nash Edgerton (Joel's brother) is often very and unnecessarily violent, (including someone getting their toe chopped off by a Beatles-loving drug lord), vulgarly sexual, and filled, not just with profanities but exceptionally crude blasphemies.
Even if you cut it to play on TV in the 1970's during the family hour, and even though it is a fast paced complex story and occasionally amusing, there is no real point to the convolutions and travails we watch this poor man endure.
I liked Oyelowo as Harold. He has good comic timing and is kind of sweetly adorable. Though Harold does contribute to the chaos, his actions are understandable given the nefarious characters who have placed him in a completely untenable situation. I’ve seen Oyelowo in drama and comedy and he has now demonstrated he can carry a leading role. I would love to see him tackle a more worthy project.
Charlize Theron (undoubtedly an accomplished actress who can do comedy, drama, sci fi, action and schmaltz in such varied movies as: Prometheus, Monster, Sweet November, and Atomic Blonde) as Elaine is her usual sexy, crude and simulateously charming self (though she was much better on the streets in Atomic Blonde than as a boardroom killer here.)
Joel Edgerton is Richard, Harold’s duplicitous, cuckolding boss, an office hustler you can’t wait to see get his comeuppance.
But I think my favorite character was 
Mitch, played by Sharlto Copley (the lead in the off beat sci fi District 9, King Stephan in Maleficent, and Murdock in 2010's A-Team feature). Mitch is Richard’s brother. Mitch is a reformed mercenary, now a mission worker in Haiti, who Richard bribes to first rescue, then to murder, Harold, dangling the prospect of cash for the orphans now in Mitch’s care. There is a surprisingly touching and thoughtful interchange between Mitch and Harold about God. Harold is devout and prays for deliverance while Mitch does not believe in much of anything. It is unfortunate that one of the funniest moments in the movie is at this point and has been played in the trailer. Mitch is the only aspect of this movie which deserves any contemplation. A hitman turned philantropist, who is suddenly confronted with the moral conundrum of whether to sacrifice one innocent man to alleviate the suffering of a hundred children. The difficulty is compounded by Mitch’s express declaration that he is an atheist. Realistically Mitch has no reference point except his own conscience, the surprising turns of events which can only be described as Divine intervention, and the admonition from a man Mitch does not believe Divine that "Greater love hath no man…." There is a nice resolution to this little subplot but does not make up for the vacuousness of the rest of this movie.
Had Nash Edgerton incorporated more underlying philosophical consideration into the filming, Gringo might have elevated itself towards Pulp Fiction territory. As it is, it is merely a forgettable romp.
Gringo is "appropriate" for only a slender demographic of the adult population – mature grown ups who, nonetheless, can find a few laughs in exceptionally crude humor and violence.
I say go find What’s Up Doc? It is a far funnier movie and one you can show the entire family.