..... neighbor bad boy and girl hooking up or guy meeting back up with friend's little sister and hooking up?

I really liked the book Cathryn by Shannon Waverly and wouldn't mind reading some more like that.

Bare Necessaties-can't remember author. It's a Blaze and hero has always secretly lusted after his buddy's younger sister who was too young.  She finally grows up and big brother asks hero to keep an eye on her when she moves to the big city.

Lora Leigh has that storyline in her SEAL series but I can't remember which book it is.

Sherri

also Born to be Wilde by Janelle Denison

Joel Wilde, an ex-Marine turned security specialist, is asked by one of his Marine buddies to guard his sister Lora because he is afraid that people he owes money to are going to hurt her. Joel agrees to keep his mission secret, and with a history of uncommitted relationships, decides in advance to keep things with Lora strictly professional. But after some men attack her, Joel is forced to tell her the truth, and being alone together in a remote cabin does not exactly lead to "strictly professional" behavior. The sex is hot and frequent, with no love declarations made, even though they are increasingly felt. A secondary story line involves Lora's friend, a single mother who falls for her daughter's math teacher. Denison sensitively pairs men with commitment phobias and women willing to wait, creating a good read with sensual sex scenes.

In Lora Leigh's it's in the 1st 2 stories..the anthology which I can nver remember! but it's Reno and Raven and the 2nd book(1st 'big' book) dangerous games with clint and Morganna...clint / raven are brother/sister and reno/morganna are brother sister and both girls wanted the guys early on but both of them were Seals..Clint was probably the badder bad boy though. both these books are pretty explicit like erotica, esp dangerous games..hoo boy!

this was also a common theme in the seris type romances like harlequin/silhouettebut not sure which specific titles..I know I've seen some and they were probably from the 90's maybe?  If I  come across any I'll try tofind this thread and post them!

Dangerous Games is the title of one of the Lora Leigh books that has that theme.  It's an erotic romance so if you're anti super-steamy I wouldn't read it.  (but it's really good, lol!)

Taylor's Temptation by Suzanne Brockmann.  And IIRC her Night Watch has a interesting twist to that theme a well. 

After the Night by Linda Howard

Fire and Rain by Elizabeth Lowell

This one is iffy, but the *secondary* romance in Susan Andersen's "Be My Baby" is a hero's friend/little sister combo, and the main pairing is good, too, so I recommend it for both couples.

Katrina

The Diaries of Miss Miranda Cheever- I think by Julia Quinn is cute.

Dang, this is a good one and funny because I was just looking at books earlier that had a few of these themes I'll check my Library and see what other ones are good.

Sadly, I've read quite a few books with this type of theme, either they were already mentioned, or I plain forgot them:)

Too Wilde to Tame is also by Janelle Denison. 

It is about a little sister and her brothers' and cousins' close friend getting together.  It is part the the Wilde series, and I thought it was good.

I just fi nished a Blaze by Stephanie  Tyler the other day that had this theme - Beyond His Control.