They'll call it a smirk. Biden was demonstrating what a lot of people must have felt when confronted with complete fiction.
I'm sure Biden had no doubts how many people were thinking the same as he when Ryan tried to suggest he and Romney would be more bipartisan and reach across the aisle.
All Ryan could do was repeat his Obama blame list and the Romney Ryan pie in the sky, no details "plan".
Note that Biden told him that Reagan gave details.