I managed one serious picture before it all went to hell.
Not really sure why this is happening but my guess is that Brock figured that having a pet helps pick up regular girls so having a Pet would help pick up kinky girls. That, coupled with the fact that Gary needs to get out more, made Brock choose him for the outing.
Not really sure how he got Gary to go along with it. Oh well, it's not serious/canon to the comic. Just something ricockulous.