I found this information from a fan of runningman. (From an instagram that I forgot what the account name is, sorry)

The admin said that Gil said 'jesu sshi' which is 'sister-in-law' in Korean.

The 1st will be the scene when Jihyo and Kwangsoo in a taxi and Jihyo called Gil. Then Gil said "Oh, jesu sshi" and if I'm not mistaken, Jihyo replied "yes" to him.

The 2nd will be the scene when they revealed that Leessang is the real culprit and they showed how Leessang planned the crime. Gary was afraid that Jihyo would wait for him for such a long time. If you listen carefully, Gil said "Jesu sshi is not the one who is crazy. You're the one who is crazy"

There's a possibility that Gil only said that to tease Gary, yes. But it's just kinda weird with the fact he said it naturally like he said it all the time and Jihyo also accepted it like she often to hear that.

Anyway, as a MCshipper I'll be thrilled if they really is dating hehe^^