Though the Boston Terrier coat doesn't mat or tangle much, hair snarls sometimes develop--especially when dead hairs get tangled up with healthy ones instead of falling out. The first defense against Boston Terrier coat tangles, of course, is consistent brushing!
Some owners do like to use de-shedding tools to reduce the development of tangles or mats (and to minimize shedding in general). The tool's fine, sharp teeth reach down into the coat and pull out he dead hairs. With de-shedding tools like a Furminator, Boston Terrier coats obviously shed less--and in turn, don't get tangled as easily.
The problem with de-shedding tools is that they often remove healthy hairs along with the dead ones, which can make the BT's coat look uneven. So if your Boston Terrier's coat does get tangled, the best way to deal with it is to use your fingers. This method is more time-consuming, but it's less damaging to the coat. Simply use your thumbs and forefingers to separate the hairs, going strand by strand if necessary. If you like you can spray the snarl with de-tangling solution beforehand to separate the hairs. With extra-stubborn tangles, use scissors to cut them in half (or even fourths) to get the untangling process started.
And if a tangle is impossible to remove, the only option left is to cut it out with scissors--but this should be the last resort.