Why are tattoos deemed as slag tags?

reason im asking is im about to undergo major surgery and ill be let this time with five points where the surgeon will make incisions for key hole surgery and after that ill be going under abdominal surgery leaving me with a massive T shape scare ..I want to cover it after with a trailing ivy/vine with butterfly's covering the key hole scares.....my family aren't really supportive and my boyfriends saying its a slag tag im thinking of getting........so is it really though of as slag tags.