Responses
Examples to illustrate (yep, educational purposes, sure):
Matching! Sexy!!!
http://www.mangago.zone/read-manga/kocchi_muite_ai/mf/c002/35/
Matching! Excuse me while I mop up my nosebleed!!
http://www.mangago.zone/read-manga/you_re_my_loveprize_in_viewfinder/mh/v06/c035/14/
No matchy #－.－)
(Spoiler - it's from this manga)
http://www.mangago.zone/read-manga/miraiken_de_ai_o_tsumugeba/uu/miraiken_de_ai_o_tsumugeba-chapter-3/35/
Take off your damn clothes, senpai. It just looks ridiculous when one person is totally naked and the other is fully clothed!!! Half and half is sexy - uke naked from waist down, seme from waist up (although I do worry about the zipper, as has been discussed by others). But they have to match, this fully-clothed-seme/naked-uke thing is so common and it always distracts me from being able to appreciate what they're doing!