1. Didn't have room for two pairs of shoes in their luggage. Goes out to all fancy dinners...in running shoes.
2. Too tired to go sightseeing because they got lost on their morning run and saw everything already.
3. Hoards all the bananas from the complementary breakfast buffet claiming you never know when runger might strike.
4. Looks like they're wearing a permanent pair of white running shorts (or sports bra Kara Goucher style) and socks at the beach.
5. Keeps knocking on the hotel wall to let your neighbors know it's quiet time. It's 8pm.