The inadvertent slow roll

I was playing the $1/$2 tables this weekend and at a table with a few drinking novices, a few experienced players and a few inbetween. Basically a pretty good mix.

The short story is that at showdown with three players left an inexperienced player, first to show, looked at her hand for a bit (I assume to figure out if she won without revealing her hole cards) then mucked face down. Next to show quickly flipped over medium pocket pair for trips. The last to show may not have been paying attention ( I wasn't in the hand, trying to flag down a server for more adult beverages ) and finally showed the cards completing a flush and having the winning hand.

Trips thought he was slow rolled and it got ugly fast. The floor had to come and calm things down.

As a beginner i can put myself in the other persons shoes and see the need for a few seconds to determine if I (or in this case him) rivered a straight flush or whatever, instead of just having a pair or something like that. But I also wouldn't want to purposefully slow roll anyone.

I assume the best way to prevent a slow roll is to show your hand at showdown immediately and let the dealer sort out the winner.

Have you ever been slow rolled, and how did you react?