I suppose for me it's the bicycle shaped objects that i had the misfortune of assembling in my student/younger days at halfords. The Shockwave branded ones were particularly sh**e and made the Apollos look reasonable.
Not a criticism of the brand as such, but I had a professional encounter with someone from Pace a few years back, where i went to some effort to reply to them giving an opinion/advice on something they had asked (mainly because I was excited about being asked by a brand I really respected), and they didnt even bother to acknowledge it despite certainty that they had read it. Now when I see their products, I associate them with that incident and it has put me right off.
There are also brands that I prefer not to use as a completely personal preference, like I always go with a Shimano groupset on a build rather than SRAM etc. That's probably likely a success (or not) of their marketing departments over the years though.