Just ask him “What’s the color of the boat house at Hereford?”
I have a friend who was a bartender. She say she never served a guy who wasn’t a Seal, Ranger, Green Beret…
I’m not sure I believe her. Maybe you should ask her what color the bar stools are in the soldiers’ mess at Fort Bragg.
Very few NSA civilians do anything resembling spying. It’s mostly math/science nerds and pencil pushers.
Yeah, I used to work with (but not for) various intel agencies. If you stop to think about it, anybody doing true spook work knows better than to advertise the fact. Hence all the greeting card salesmen. 
The old Greeting Card Salesmen Trick eh?
Well, that was kinda her point. They all claimed that shit. She says she never had a guy tell her they were in the military and drove a truck or washed dishes. Heros, All. 
I’ll bet she wasn’t really even a bartender, that was just her cover story.
The irony of this is that de Niro mispronounces Hereford as “Hear-ford”, rather than “He-re-ford”.
Well, the rules are different. Special forces have a wide latitude in uniform regulations and gear. They’re allowed full beards, for instance, and they often modify their uniforms for personal comfort and/or to better fit in with their environment.
But… can they wear Vibram Five Fingers? Evidently, the answer is yes. You can find this picture referenced on DoD PA websites, although I can’t seem to find the original.
(The guy referenced in the OP is full of shit, though. I bet he saw this same article).
Would you believe…?
Well it depends. Special Forces means a very specific thing, Army Green Berets. “Special Ops” can mean a myriad of things. A cook assigned to Special Operations Command can say they work in Special Ops. Even with the tip of the spear guys most will only have relaxed grooming standards when on deployment not their entire career. SEALs and Delta may train with unconventional weapons but most that fall under SOCOM will use US weapons. Each level within the special ops community has different kinds of rules.
A lot of the gear “specifically designed for the environment” is just COTS hiking gear too. In Ghost Wars Steve Coll described how the first team in Afghanistan after 9/11 just drove to the Arlington REI to get gear. Should have said he wore Salomon Quest though.
Not entirely impossible, one can get in on a waiver at 17, then basic, advanced infantry course, then finally RASP [Ranger Assessment and Selection] and His Noodliness willing, you pass everything [and have everything needed like citizenship and suchlike] you is special forces. One hitch, 6 years and one can have a 23/24 year old operator that is now a member of the DD214 club. Sort of ditto for Seals. Personally, if I was going to be military, I would do what mrAru did and stick it for the full 20 [which is the only thing keeping my lame ass alive, Tri-Care for Life … ] so he gets what he contracted for back in 1983 - included medical in retirement, 50 percent base pay, he got some sort of education deal.
“Then why be one?” 
Years ago I used to work in computer forensics consulting. I had a number of colleagues who had previously worked for the NSA, CIA, FBI, and other intelligence or law enforcement agencies, were ex military, or came from firms associated with the military-industrial complex like Haliburton, Kroll, and Control Risks. One the one hand, it could be made to sound very exciting. We are travelling around a lot, often involved in high profile cases people see in the news, frequently work with law enforcement, and my particular company had a bit of a penchant for drinking and partying and hanging out in strip clubs.
But the reality was most of the work was actually pretty boring. Most of it consisted of sending people to an office to collect a bunch of hard drives to bring it back to other people to feed the contents of those drives into software so lawyers and forensic accountants could review it.
From what I could tell, intel agencies did a lot of the same sort of work, except they had to do it from inside a hot shipping container in some foreign desert.
That may have been intentional - afterwards Stellan Skarsgard asks DeNiro “What color is the boat house at Hereford?” and DeNiro replies “How the hell should I know?”
I don’t think so. De Niro’s test is to see whether Sean Bean was in the SAS, which is based in/near Hereford in the county of Herefordshire. By pronouncing it as ‘Hear-ford’, De Niro is basically testing whether Sean Bean is a British person, or at least someone with some familiarity of Britain, as the average British person would know how it’s pronounced. Really, Sean Bean (the actor) or someone else in the film crew should have corrected De Niro.
But I’m saying that DeNiro had Bean so completely cowed that Bean didn’t even notice that DeNiro was mispronouncing the town name - if he had, he would have known that DeNiro was bullshitting him and could have challenged him back.
But you’re right, it’s probably just how DeNiro read “Here-ford” in the script.
It’s not the first time DeNiro says “Hear-ford,” as he asks “boys at Hereford?” of Bean when he’s sussing out his background, to which Bean gives a non-committal reply.
But ISTM that “Hear-ford” is exactly how an American CIA agent would pronounce it, so I’m not sure it’s incorrect. I wouldn’t expect the character to be familiar with a local pronunciation.
Alas, “American mispronounces name of English town despite having been there in person” is not, from this side of the pond, a concept which requires much, if any, suspension of disbelief.