Just all the times over the years that Foggy has accidentally turned Matt on without realizing it. Could be anything - a full body hug that lingered too long, a finals stress-relief massage, he overheard him getting off on his own or with a partner, a late night call with Foggy’s voice low and laughing in Matt’s ear. Anything goes.

Bonus - Foggy eventually catches on to the affect he can have on Matt.