Being a tough guy is for the most part, an inborn characteristic. It's almost impossible to become tough, but being thought of as tough is usually just as good. If you want to be seen as tough, then all you have to do is change a few minor aspects of your appearance and demeanor.
First, stop shaving. Tough guys don't care about their looks, they don't need to impress anyone. They're too tough to care.
Second, if you're a tall guy, then that's good. The ideal tough guy is someone so tall that ice forms at their peak. If you're not tall, try to increase your height with a good pair of work-boots. Not combat boots, because they're not practical, and tough guys are always practical, which is why you must also always carry an extensive set of screwdrivers and pens.
Third, tough guys can like whatever they want, because no one would dare question their tastes. So, adopt into your look something peculiar, like a pink hat, a cravat, a backpack in the shape of a bunny, or if you want to really sell the badassness, a gold tiara.
Fourth. Are you wearing jeans? If you are, you're half-way there. Just cut those jeans off at mid-thigh. Tough guys aren't afraid of people seeing their knees.
Fifth, read books. Tough guys aren't just tough for toughness's sake, they're tough because they're strong physically, psychologically and mentally. So increase your brain-thinking with knowledge of stuff and/or things.
Teddy Roosevelt was a tough guy, and when he was asked to shoot a bear, he didn't, because he didn't have to, he killed that bear using the power of his mind, just by outliving it! That's a tough guy.