tag-a-long thomas Share definition Flag An uninvited person who can't take a hint they're not welcome with the group. Hey did he just jump in the car uninvited? Man, he's such a tag-a-long Thomas. tag-a-long thomas by Ponyo911 November 2, 2009 0 0 Get merch Get the tag-a-long thomas mug. Buy Now — $32.95 See more merch