Deckard finds one of those foam noodle things you play with in the pool while shopping with Luke for a mission, and Deckard challenges him to a noodle duel.

Luke video calls Deckard while he's at the gym just to flex his muscles.

Luke refuses to yell at stupid people driving in traffic in front of other people but you can see the flames of hell in his eyes. Deckard, on the other hand, just starts repeatedly honking his horn.

Whenever Deckard comes over to Luke's house, he isn't invited, he just finds his way in. Luke's daughter says hello like its normal for him to break in (which it is) and every time Luke gets home from work, Deckard is waiting there for him.

One time, they saw each other on the road and started honking at each other as a competition. It would go like this:

Beep.

Beeeeep.

Beep beep.

Beep beep beeeeep.

Until one of them gets stopped.