In it, everyone piles into some van and there's so many people Kurt has to sit on Puck's lap. This makes Kurt uncomfortable so he holds onto the seat in front of him. After a while most of the van falls asleep and Kurt eventually relaxes enough that he starts disturbing Puck and making him hard. They both get hard and I don't remember if they both actually get off, but I know that Puck wanted to and Kurt was kinda wanton/cautious about it.
If anyone can totally help me find this, that would be great. =D