Delinquents

Shoujo:
http://www.mangago.me/read-manga/faster_than_a_kiss/
http://www.mangago.me/read-manga/life_is_short_delinquent_youngster_love/
http://www.mangago.me/read-manga/atashi_no_banbi/
http://www.mangago.me/read-manga/rensou_mode/

Yaoi (one of the mc is a delinquent):
http://www.mangago.me/read-manga/hatsujou_animal/
http://www.mangago.me/read-manga/violence_na_kimi_ga_suki/ (delinquent uke)
http://www.mangago.me/read-manga/i_don_t_dislike_you/
http://www.mangago.me/read-manga/dou_imo_nara_nai/
http://www.mangago.me/read-manga/u_don_t_know_me/ (uke)
http://www.mangago.me/read-manga/koibito_wa_hatsujouki/ (1st story)

http://www.mangago.me/read-manga/crows_zero_borderless/ it's a dj though, so if you don't know the original movie "Crows Zero" it may be hard to follow (it's about a school of delinquents :P)

Yankee-kun to megane-chan has a lot delinquent or ex-delinquent characters. It's shounen but has romance as the second genre (I think). The first one is comedy. http://www.mangago.me/read-manga/yankee_kun_to_megane_chan/

http://www.mangago.me/read-manga/devils_honey/

(▰˘◡˘▰)

Shoujo
The male lead does qualify as a delinquent, playboy and someone with a trauma in his past (something he shares with the female lead too)
It is one of my favorites, if you haven't read it, you really should. I don't think that you'll be disappointed and the end is really fulfilling.

http://www.mangago.me/read-manga/mars_souryo_fuyumi/

yaoi delinquent list
http://www.mangago.me/home/mangalist/20941/