...which,
come and play!
Gen
Treachery. The boys are hiking up a steep mountain and Dean's sneezing all over the place and kinda dizzy. When the path gets particularly treacherous, Sam makes Dean hold his hand.
Evasive Maneuvers. The one where Dean goes to interview a victim, and Sam has to come pick him up because he's a sicky, feverish, sneezy, fainting mess.
On Hand. In an attempt to keep police off their trail they decide to burn Dean's fingerprints off. Of course he happens to come down with a sneezy messy cold and needs Sam to take care of him (since his fingers are all sore and bandaged and unusable).
Slash
The System. Dean pretends he's pretending to have a cold, and Sam pretends he's pretending to worry.