Years ago, I collected Colts and defined a BBQ gun on the Colt Forum. If I remember, it was:
Forty caliber or better (357 Magnum is acceptable, as are some 9mms), capable of taking down whatever was on the grill. Preferably a revolver made by Colt or S & W, although 1911s, 1935s and 1909s were acceptable. Preferably engraved (Wolf & Klar a plus) and/or nickel plated. Grips of a natural material, preferably animal-based. Leather custom or from EPS, Heiser, etc., carved or basket weave. Belt, boots, and hatband should match leather gear. Matching pocketknife a plus. Extra points if you took it from a man trying to kill you.
Not really BBQ guns but matching Colt SAAs with real ivory grips (pre-ban):
1901 Colt Bisley, shipped 1901 to Mexico City, Cottage engraved on the "Rez", carved real ivory with ruby eyes.
.41 Long Colt SAA, 1906, real pear grips:
Another showing some leatherwork as well (EPS)
And a 1911 just for kicks:
Here in eastern WA, wearing guns to a BBQ is still acceptable (don't know for how long....)