In the big picture of things, true and enduring Christmas traditions don’t come around very often. So from that perspective you have to credit actor-writers Joe Sears and Jaston Williams for successfully spiking the fruitcake in the holiday installment of their Tuna play series. Sears and Williams make fun of small-town Texas, but they show it love too, via deft comedic timing and tour de force mastery of all characterizations — both sexes, and all ages. A Tuna Christmas is now 21 years old and still going strong, and as simply stupid as it all looks — a disaster-prone production of A Christmas Carol and a Christmas lights yard display contest are the central events here — Sears and Williams pull it off. Fact of the matter is you can’t help but laugh. Direction is by Ed Howard, who is also a contributor to the script.