The kissing thing can have multiple interpertations in Japanese because it is such a context-sensitive langauge.
Goku basically saw Trunks give Mai a Senzu by mouth-feeding her, and he said he's never kissed Chichi "that" way. Which is a legitimately strange way of "kissing" someone.
It's Goku and Vegeta talking past each other.
It can be interpreted of Goku having never kissed Chichi, but that's also kinda strange considering they have two kids and ignoring context of the exchange. Maybe some Japanese speakers can correct me, but that's what I've seen talked about.
That's not what happened.
Goku was wondering why Trunks put his mouth on Mai's mouth. Vegeta asked him if he's ever done that and he responded "of course not".
You don't need to kiss someone to have sex. There are people who don't care for it. It's not that big of a deal like people are making it seem. If Chi Chi wanted to kiss him on the lips, nobody's stopping her. She kissed him on the cheek before & Goku didn't react at all. He's not an intimate person.