"You'd risk your life just for a picture? Just so you can upload it on social media? Or do you do this because this give you 'the rush'? How is this sensible?" said one commenter.
"Insanely stupid stunt. You two will end up dead if you keep this clout chasing up," another added.
One called the stunt "irresponsible" and said it would lead to copy-cat acts, while another criticised Miguel for putting his girlfriend in danger by not being the one outside the train.
However, Raquel said on Instagram: "The guy didn't put me in danger, I'm pretty independent, and I do what I feel comfortable with."
They later stated that the train was "almost not moving".
Dangerous social media snaps are a growing trend, according to recent studies – particularly in risky selfie-taking.
A study published in the Journal of Family Medicine and Primary Care last year found that 259 people worldwide had died while taking selfies since 2011 – most commonly by downing, being hit by traffic or falling.