There have been a few that could qualify as frivolous. Probably the most frivolous was while buying a Mossberg 930, my son noticed a Witness in 10mm. I was familiar with them and on learning that the price was under $500, hardly looked at it at all before adding it to the day's bill. I had already committed to the 930, but thought that the 10mm Witness was a rare thing so just bought it for no real good reason. Turned out to be a nice gun. I had that longer than I kept the 930.
Frivolous is debatable. If self defense were the only criteria one large bore pistol (or DA revolver) and one shotgun would do the job with perhaps a second micro size pistol for concealed carry. The 1911 .45 ACP and .380 ACP plus a tactical 12 gauge suffice. Also got a M9 pistol and .357 GP100 revolver. Other than the .380 ACP, they're all calibers and handgun types I carried in the past. The M9 and GP100 could justifiably be alternatives to the 1911. Necessary for my primary use? No. Wouldn't go so far as frivolous though.
The 5.5" .45 Colt Blackhawk is the odd one out. It's simply a fun revolver. Could be used for self defense with the heavy loads I put in it, hotter than the common "cowboy" stuff, but wouldn't want to rely on it for any more than six shots. I'd need a New York reload. Patton realized this when he carried a .45 Colt SAA during the Punitive Expedition in 1916 that pursued Pancho Villa into Mexico. Reloading one in combat sucks. He acquired a second one which he gave away at some point after WWI to a movie actor he admired that had entertained troops during the war. It was replaced with a S&W Registered Magnum about 1935, forerunner of the Model 27. If any of them are "frivolous", it would be this SA .45 Colt Blackhawk. Nevertheless, it's a fun one to use at the range.
John
Had lots of frivolous ones.
My favorite excuse is , "Well, I already had a scope and I needed a gun under it."
Shucks. I have bought guns because I bought reloadable brass for a caliber I wanted years before.Uh.....I thought I was the only one...