Some of you have asked before how to take your character's shirt off, so you could see the tattoss you've purchased.
As for Franklin, there's an option to make him wear his underwear, and after selecting that, you could easily just put on some jeans or other stuff you want. Hope this helps.
Also, sorry if this has been mentioned before, but I think this is a neat little tip for those who don't know.
Or just use the "No Top" option under the "Tops" section in your wardrobe.