Texas graduate and fan here, and just fyi, no real Horns fans really care about "horns down" silliness. It's actually viewed as nothing more than good fun by pretty much everyone I know.
This all started a few years ago when a Longhorns wide receiver, Mike Davis, scored a TD at Texas Tech. He holstered his six shooters (TT hand sign is "guns up") in the end zone and was promptly flagged for "taunting" by the officials.
Like pretty much everyone else in the conference did before without issue, Tech fans and players had been doing horns down all game, so naturally Mack Brown got pissed when his payer was flagged for basically doing the same thing to the opponent. All Mack - and Texas fans - was pissed about was inconsistency by Big 12 officials (of course, lol).
So, of course, it being Texas, Mack's getting pissed about Tech players doing Horns down the rest of the game became news and message board fodder. Seems like it just kind of grew from there.
So, in summary, Texas fans really give zero sh!ts if you do horns down. OK, cool. Hook Em.