Most patriotism in WWI was not coerced. It might have been encouraged by the government's propaganda efforts, but it was not coerced. However, there were some incidents of people being coerced to at least act in ways that were outwardly patriotic.
Perhaps the most coercive tactics were aimed at selling war bonds. Loaning money to the government was seen as a way of showing one's patriotism while giving financial support for the government's war efforts. People were severely pressured to buy these bonds. In other words, they were coereced into acting patriotically. As one textbook (The American Pageant 11th Edition, p. 730) tells us, German-Americans might have their houses defaced with paint if they did not buy bonds. At least one person was threatened with being hung if he did not buy a bond.
One can also say that many immigrants were coerced into giving up their native cultures so as to appear more American. My maternal grandfather was of German ancestry, born in 1911. His parents spoke German to one another before the war, but then stopped during the war and never started again because they did not want to seem unAmerican.