Or maybe they wanted/needed to know his whereabouts for some reason? Maybe they were concerned and wanted to make sure he arrived home safely. I keep remembering one of the men in the party mentioning Brenda's car/truck being parked in a different space at the end of the evening. Did she leave for a short time and then return to Dad's? Why?
It would seem possible that the pizza partiers "DRUGGED" DW (Zanex in his 'shot') because they (Rich,Keith) wanted to party with Denise,Barb and do drugs.
DW was not a druggy and they were probably afraid he would 'narc'.
So, when he starts getting 'hazy', Brenda drives him home, with someone (Barb) driving DW's vehicle. It's only 5 min away from Dad's.
Later, when something happened to Danielle, they all decided to hang it on DW, since they knew he wouldn't remember what happened anyway.