Can my physical appearance affect the airport security officers decisions? How is that possible? I mean what would they put in their reports? that I was wearing a shirt saying "I <3 Bin Laden" ?
There are several reported instances of people not being allowed to board (or being kicked off) planes because of their T-shirt. These include:
A man being refused boarding in the UK due to a picture of a cartoon Transformer holding a gun on his T-shirt being a security risk (yes, really, you can't make it up).
A man denied boarding to a Qantas flight for wearing a T-shirt claiming George Bush was a terrorist. The man was not George Bush.
A man denied boarding to a Delta flight on the basis that his T-shirt satirizing various TSA procedures and (alleged) security theatre 'made passengers feel uncomfortable'.
An Iraqi peace activist denied boarding in JFK due to a pro-peace slogan (written in Arabic) on his T-shirt.
Though I had remembered a couple of these examples, more were not difficult to find, so T-shirts are clearly serious business.
But in answer to your question, there is certainly an increased chance of you being denied boarding if you wear that T-shirt, especially if you are also carrying a gold bar and a bazooka. Perhaps stick with the bulletproof vest.
Your friend would not be denied on the basis you have given. The point of the search is to examine you and your belonging for dangerous articles, not to check if you have a Koran or if you have a poor sense of fashion. I will not speculate further on the reason for his denial to the secured part of the airport, but a messy beard and a book is not the reason.
In principle if you were wearing a provocative t-shirt, you could be selected for a more detailed examination (which would include removal of outer clothing and a hand search of your effects in private). If it was particularly provocative, the police may arrest you on the basis you are committing a breach of the peace.
You ask one main question and three sub-questions:
Can my physical appearance affect the airport security officers decisions?
How is that possible?
Screeners are human and react emotionally. A provocative appearance is more likely to, well, provoke a response. This will be more true in places like the U.S. where airport security screeners are less well trained or disciplined.
I mean what would they put in their reports?
"Passenger looked suspicious."
that I was wearing a shirt saying "I <3 Bin Laden" ?