1) Hearing James Marsters (Spike) speaking in his natural accent.
2) Wonder Woman Golden Age crack
3) Catching Jamie Bamber (Apollo) using his natural British accent on Law & Order UK.
4) That there is a Law & Order UK in the first place.
5) Americans driving on the parkway and parking on the driveway.
And for a grand finale to confuse you all, there's this old classic puzzle I first saw when I was but a nipper:
3 men go into a motel. The desk clerk said the room was $30, so each man paid $10 and went to the room. A while later, the desk clerk realized the room was only $25, so he sent the bellboy to the 3 guys' room with $5. On the way, the bellboy couldn't figure out how to split $5 evenly between 3 men, so he gave each man $1 and kept the other $2 for himself.
This meant that the 3 men each paid $9 for the room, which is a total of $27. Add to that the $2 the bellboy kept and the total is $29. Where is the other dollar?
And no, it's not taxes.