For some, including this critic, The Swearing Jar’s conventionality is a high hurdle. To synopsize it is to evoke a tedious dramedy: a woman stumbles onstage and welcomes the audience to her husband’s 40th birthday, the background to which is then given in flashbacks involving a pregnancy announcement, a meddlesome mother-in-law and a terminal illness. But the play helps us grinches through our preconceptions by consistently hitting the mark with its dialogue. Its two leads, especially, young marrieds Simon and Carey (excellently played by Andrew Pifko and Janet Porter), spar with each other in an authentic and witty way. Everything surpasses cheesiness until the finale, when the play’s titular motif — which sits on a shelf in the middle of the stage throughout — might as well turn into a giant hunk of gruyère.