Early on in my lifting days, in the early days of bodybuilding.com, there was a frequent poster, "Abominator," who had more posts than RJ's All Stars combined and immortalized his "Three Stages of Shirtlessness."
Also known as Skip and Skippy Polar, the ultimate muscle geek, he went on to co-host PBS's "Star Hustler" (now called "Star Gazer ?).
He lived my childhood dream, not just of being muscular, but of being...a planetarium director! I was a geek kid who frequented Miami's Museum of Science, home to "Star Hustler's" Jack Horkheimer. Skippy actually worked for him, became planetarium director at my college alma mater, and then succeeded him.
Quoted from Skippy:
"Ok, you've lifted weights for a while, and are starting to see some results. So you're now confident enough to be seen around the house (briefly) without a shirt on. After a few positive comments from roommates and/or relatives, you're no longer overly self-conscious about being seen shirtless and you're ready to move to stage #2.
You now do things like mow the lawn, take out the garbage, and wash your car "sans camisa". A few more positive comments from friends and relatives push you to stage #3. You also find that you spend a majority of your time at home shirtless.
This is essentially the final stage. Whenever it's warmer than 75 degrees outside, you don't even bother putting a shirt on. You'll drive places, get gas for the car, workout, do your laundry at the local 'laundro-mat', or even go jogging shirtless. Whenever you play a team sport where it's "Shirts vs Skins", guess what team YOU'RE on. You actually ENJOY warm weather; eagerly awaiting any opportunity to take your shirt off. When Halloween rolls around, your costume choices usually involve characters who don't wear shirts (e.g. Rambo, The Incredible Hulk, Tarzan, professional wrestlers, or even rappers (like LL Cool J, Lil Wayne, Lil' Zane, Nelly or Marky Mark). Every so often you'll be seen randomly posing in direct sunlight and glancing at your reflection in car windows. Normal people define this trait as narcissism, but who cares? You're all that AND a bag of fat-free nachos!
At this point, you never wear a shirt at home, except of course when important company comes over. Oh...and in rare cases such behavior leads you to a 4th Stage (which I like to call Brouwer-Todd Syndrome) where you find yourself entering bodybuilding or physique competitions, becoming a fashion or fitness model, posing for calendars, or possibly taking a job as an exotic dancer, but that's a topic for later discussion."