I'll go with the theme and mention a hostile crowd rather than a completely apathetic crowd (like the one I saw when Tommy Shaw opened up for Rush in 1988).
The most hostile crowd I ever saw was when The Cult opened up for Metallica during Metallica's 89 shed tour (I saw them at Popular Creek in the Chicago area). . While they weren't necessarily angry or particularly aggressive, they did start up loud "FUCK THE CULT" chants throughout their short set. The Cult played a decent enough set (I guess), but they were a bit too hard rock for the thrash fans Metallica was focusing upon at the time.
And it wasn't necessarily hostility, but when I saw Ozzfest 97 at Alpine Valley, Marilyn Manson wound up cutting their set short because the fans would not stop throwing stuff everywhere. I don't know if it was a hostile reaction to Marilyn Manson (who really weren't suitable for the late afternoon set they god--and they were sandwiched between Type O Negative and Pantera), or it was fans blowing off steam due to the long day.
One of the most interesting individual fan reactions I saw took place in 1991 when I saw the band Ratt. Midway through their set, Michael Schenker joined them on stage, and they closed out their regular set with a cover of Lights Out. A fan near me just went insane with joy--and yet he was also pissed that very few people around him knew the song. Needless to say, that fan was inebriated.