"I don't exercise because... I guess because I'm lazy."
"I set up my business that way out of laziness."
"He's too lazy to take his car in for service."
Sometimes "lazy" seems like humourous shorthand for "I didn't feel like it." But in general I suggest we avoid using the word "lazy." There is always a legitimate explanation, a reason that will make sense whether or not we consider it a good reason. Back up and imagine you can look at the situation from 40,000 feet up in the sky. Is it laziness? Or is there a reason that can be discerned with a little more perspective?
In the first example above, a person labels himself. Having applied the label, he's got permission not to exercise, because lazy people don't. More helpfully he might say, "I don't like to exercise because it freaks me out to get so out of breath" or "I get sweaty and it seems too time consuming to take another shower." Those are statements of problems, and problems can be solved.
In the second example, she set up as much automation as possible for customer interactions. If customers are displeased with automation and the business owner feels overwhelmed by having to be more hands-on, that also is a problem that can be solved. "Laziness" was really a desire to be as efficient as possible. But calling it lazy allows us to dismiss the problem as being unworthy.
The third example, calling someone else lazy, expresses frustration and perhaps an unwillingness to understand another person's motivation. A friend pointed out that we call other people lazy when they are not doing what we want them to do. Is it helpful? Is lazy ever a constructive word? Maybe it is, when we're planning a vacation in which we intend to do very little. But even then I think it really means, "I need a rest."