Nate "My Mate Nate" Bartling set out to show poor English comprehension, but he had no problem understanding the YouTube roast he got back in the comments. (Screen grab YouTube)

A video clip of an American YouTube star posing questions to Thai students to apparently test their English language abilities and for comic effect has caused a furore on social media, with the interviewees saying they were mocked and their answers manipulated.

Nate Bartling came under fire after he posted a six-minute clip on Friday of himself asking a number of Thai students simple questions in English in front of a building where famous cram schools are located. It was meant to test the students' understanding of English by asking questions to determine whether they could answer back correctly.

The former American missionary who speaks Thai is now famous for his alter-ego "My Mate Nate" and has almost 1.4 million subscribers on his YouTube channel.

A number of Thai students complained online that they felt humiliated by the clip. Some also said they would stop following his programme.

However, some users agreed with Mr Bartling that poor English proficiency among Thai students is a fact and the teaching system needs to be improved.

In the video, Mr Bartling asked male students: "I'm on my period. Do you have a sanitary tissue? Are you on your period too?"

The male students replied "yes".

He later greeted students, "You look absolutely terrible today" in a casual tone, and many of them, looking confused, replied "thank you" or "I don't know".

He explained at the beginning of the video that he wanted to reflect the failure of English teaching in Thailand's education system which emphasises learning grammar rather than speaking and listening skills.

"Students in this country learn how to read and write in English before speaking and listening. It's an unnatural way to learn a language and it is the main reason why they cannot communicate efficiently," Mr Bartling said in the video.

The video went viral quickly and received 941,000 views by early Monday. However, it drew 3,600-plus "thumbs down" and a slew of negative comments after one of the students who appeared in the video tweeted a message accusing Mr Bartling of distorting the truth with the intention of making them look stupid.

One twitter user, @cherryluvjs, claiming to be one of Mr Bartling's interviewees, said the YouTube star came up to her and her friends and asked the question of where he could find a sanitary towel.

"We replied to him in English, but he did not put that in the video. After that, he asked us what we thought of our education system. We answered in English, but he wanted us to answer in Thai," she tweeted in Thai.

The girl added that, in fact, many students who answered his questions properly were told by Mr Bartling to act as if they couldn't understand him.

Summerbig Loveoale Sawaddee, a Facebook user, said in the post in Thai: ''I think all Thais should admit that our English learning system needs to be improved. I reckon English competency among the majority of our students is not on par with neighbouring countries.''

Another Facebook user, Lek Mayne, wrote: ''You should respect all of us. That's not funny at all. What if I ask you a question in Isan (northeastern dialect) language?"

Jack Brown, a British YouTuber who speaks Thai, also posted on Facebook: ''Nate... why??? You're a guest in this country. It's not necessary to intentionally humiliate people. If you wish to inspire change, then do it by educating people, not by making a mockery of them.''

Recently, Mr Bartling uploaded another clip to clarify what had happened during his stunt. He admitted that one student's reply in English was not included in the clip.

''My goal is to point out the problem in Thailand's English learning system in the whole picture, not individuals. We need changes to fix it,'' he said.

Yuwadee Yoosabai, director of the Office of the Basic Education Commission's English Language Institute, said she could not comment on the clip and on the proficiency of Thai students' English as she had not seen the video.

"Nevertheless, I think we can use all criticism to improve ourselves. The best way to let criticism drive you is to be open to hearing it in the first place," she said.

Ms Yuwadee admitted that speaking and listening skills are among Thais' weaknesses in the language and need to be improved.

''Thai students are quite good at grammar, but when they have to speak English to foreigners, many cannot communicate well because they focus their learning of the language on taking the exam."

The Education Ministry is considering tweaking its English examination system at elementary and secondary schools by putting more emphasis on the speaking and listening exams rather than multiple choice tests, she said.

According to the latest EF English Proficiency Index conducted by the Education First Language Institute, Thailand's English proficiency is "very low".

Thailand is ranked 14th out of 16 countries in Asia and 62nd out of 70 countries worldwide for the population's English language speaking abilities.