SCP, SCP, SC SC SCP, SCP, SCP, SCP-173! (x2)
When I first saw him, I was really scared!
We came with 3 men and got fully prepared.

In reference to SCP-173’s official article, no fewer than 3 people may enter SCP-173’s containment chamber at once, usually for cleaning purposes due to the amounts of fecal matter and blood SCP-173 produces while unattended.Side note: Notice Glenn’s phrasing. “He.” As it turns out, Glenn Leroi has confirmed SCP-173 indeed does have a gender, and does identify as male.

Standing in the corner, there against the wall, looking like a giant white concrete rubber doll!
Then I walked to him, like really close.
I looked at his face, but he had no nose!

This is, of course, a nod to Izumi Kato’s Untitled 2004 sculpture, in which the art piece stands proudly up against a wall. Funnily enough, Kato’s figure does have what resembles to be a nose.

Then something just went terribly wrong!
And this is just the part of the 173 song.
(SCP, SCP, SC SC SCP)
There was a problem with the doors, and the electricity too!

In SCP containment breach, it is speculated that SCP-173 as well as other SCPs were able to breach containment due to SCP-079 and SCP-682 working together to gain control of the lighting and door control systems, bringing on the events of the game.

And before I knew, he was out of my view!
Standing behind my friend his back,
He killed him with one single attack!
Short after that he killed my other mate,
And then i just became really afraid.
Standing there in front of me,
And my pants came wet due I had to pee.
He didn’t move and I like “What the heck?”
And suddenly I blinked and he snapped my neck.

We all know what SCP-173 is, and we all know what SCP-173 does, but the other parts of these lines could very well be alluding to D-9341, who is the protagonist of the SCP containment breach. It is speculated that D-9341 is anomalous himself, due to his ability to “save” and “load” progress, giving the player more than one chance to survive his encounters with SCPs. In the ending in which D-9341 escapes the facility through gate A and has not recontained SCP-106, once he is discovered by MTF units, the game ends and you hear the following lines.
"Testing log ███. Subject █-████. Subject demonstrates extraordinary luck and complete mastery of even the most fatal of circumstances and an uncanny ability to predict even the most unpredictable of hazards, almost as if it has performed these impossible tasks several times before. Further testing is required to determine whether the subject should receive SCP classification."

(SCP, SCP, SCP-173!) x2
He is so cute and very brute, he wears no suit and loves pursuit.

Glenn is correct, SCP-173 does not wear a suit. Considering SCP-173 is constructed from concrete and rebar, it only makes sense to refer to him as brute. Cute subjectiveness aside, Glenn brings up how SCP-173 loves pursuit. This has often perplexed me. Why does SCP-173 pursue people, and snap their necks? SCP-173 will also make sounds of grinding concrete when trying to escape his containment chamber, so you could figure it shows some form of sentience, but that’s all up for interpretation. For any who would like to read up some more about any possible motivations, I recommend http://www.scp-wiki.net/crunch. Again. Up for the reader to decide, but it’s worth the short read.

(SCP, SCP, SCP-173!) x2
(sounds of grinding stone play)
Now I’m here alone, but I don't mind!
My two best mates I sure will miss!
173 is one of a kind
And you'll never know what he really is!
Let’s get moving, I'm out of here!
I'm so scared, I know he's near!
He'll come for me, but we don't know when!
Oh, no! There he is again!
SCP, SCP, SCP-173! (x2)
He is so cute and very brute, he wears no suit and loves pursuit!
(SCP, SCP, SCP-173!) x4
Don’t look away and never go back, cause he will chase you and snap your neck!