Why do tough guys chew toothpicks or match-sticks?

My recollection is that chewing toothpicks, as a stereotype, was for farmers, carnival workers, oil roughnecks and other extreme blue-collar hicks.

A soldier chewing on a toothpick signals that he's not some college-boy officer, and not even some factory worker from the Bronx. He's probably a country boy. He was an expert shot with his daddy's rifle at 12 years old and knows jungle survival because he grew up in a bayou. But after dodging the revenuer who's after his moonshine still, he doesn't have much respect for authority -- a real renegade. I realize that's a lot of work for one toothpick.

Scott Hall (Razor Ramon) is a little different, but similar. His original wrestling character was a Florida boy who wrestled 'gators -- a toothpick chewer if I ever saw one. He started the gimmick while playing a sexy bad guy. But we can see the problem in this match where a young woman is very excited to be allowed to rip off his pants. We can't have too many women cheering for him, so need strong signals that he's the bad guy. Thus, greased-back hair and a toothpick stuck in his mouth to show that he's low-class (and flicking it at people is a fun gimmick).

That’s a very common trope in movies known as “Oral Fixation.” It's not even limited to toothpick and matchsticks either, but also show straws, lollipops, etc.

Mostly presented to make your character look cool or badass and also a safer option than smoking as there are smoking rules in many countries too.

Alternative addiction people do exist in real life, too, and get fixated with something which doesn't harm or harms them less, like coffee instead of alcohol, or something chewable instead of cigarettes. There is even a TV trope link for that.

The reason seems obvious: "I eat you raw! All of ya!" A sign of power. Be it Kojak sucking his lollypop or dirty Harry eating his cigar. Or Buggs Bunny his carrot, for that matter. Quite sexy, actually...