This is/was clearly X.
Simply means that the circumstances make it apparent to the observer that X is true.
Without knowing the full context of the statement, I can only speculate, but lets imagine a passage such as:
She woke up at 10:30am, took a long shower, then made coffee, and sat on the sofa to read a magazine. This was clearly her day off.
One can see from the circumstances that the woman is in no hurry to get to work, or other commitments so this was clearly her day off.
The key is the word clearly, which has several synonyms in this context, such as obviously or apparently...
This was obviously her day off.
This was apparently her day off.
Or even some similar phrases:
This seemed to be her day off.
It looked like this was her day off.
"It is/was a great day to be alive" simply means that the speaker believes that this particular day was a day that he enjoyed. That is, he is glad that he was alive on this particular day. It's a fairly common phrase used to express joy about some event or experience. It is used to describe all sorts of events, from things very personal to things very general.
Like, "I looked out over the beautiful fields, filled with flowers, and the majestic mountain towering in the distance. It was a great day to be alive."
"I just head on the news that the war is over. People are pouring out into the streets to celebrate. This is a great day to be alive."
"Today we have all sorts of conveniences to make our lives more pleasant, from the automobile to television to microwave ovens. This is a great day to be alive."
It does not normally mean that the speaker has narrowly escaped death or anything like that.
"Shoot" is simply an interjection, a word used to intensify an expression. It is a very mild word. It can be positive or negative. "Shoot, I lost my pencil." Or, "Shoot, my favorite TV show is on." If used in more extreme situations it is seen as quaint or a deliberate under-playing. You wouldn't normally expect someone to say, "Shoot, the doctor just told me I have only three weeks to live." If someone did, you'd either take that to mean that he was deliberately downplaying the seriousness of the issue, or that he is someone who is particularly mild-mannered or who does not use strong language.
Best Answer
<thing> of the day is often used to mark the specified thing as the most significant thing (of that type) that you will encounter on that day. I assume that "set" is some surfing slang for "a large, surfable wave", so saying that a wave is "the set of the day" means that it is the most impressive, challenging wave that has come along that day (and no other, later waves are likely to equal or surpass it).
You'll likely hear things like "catch of the day" (biggest fish caught) or "play of the day" (most impressive sports action). Of course, other time frames can be specified too; "Storm of the century" and "man of the hour" are also popular phrases.
That was my line is normally used to mean "you just said what I was going to say".
However, that is not how it is being used here; here, line has the meaning "a course, path, or direction taken by something in motion". (see meaning 3c at Merriam-Webster.) In this exchange, the first individual is indicating that he is to blame for choosing the area, and the path, that led to his partner's death. (The second person then points out that the dead person chose to snowboard the path too, and it was his own responsibility to navigate it successfully.)