Peppermint Patty's constant companion, Marcie, calls her "Sir" and has since she first appeared in the strip by name in 1971. For a long time, this annoyed Peppermint Patty to no end, and she would continually snap at Marcie, "Stop calling me 'Sir'!", but eventually she got used to it. (Actually, the first character to call Peppermint Patty "Sir" was not Marcie, but a pigtailed girl named Sophie in Peppermint Patty's cabin at summer camp, who appeared in the same series of strips in the summer of 1968 that introduced Marcie's predecessor, Clara.) Some observers have suggested, given Patty's tomboyish tendencies and Marcie's referring to her as "Sir," that Patty and Marcie are a lesbian couple, but Schulz never depicted Patty having a romantic interest in any female character, only in a male character: Charlie Brown.
Not until a few years after she was introduced into the strip did it become apparent that Peppermint Patty had a crush on Charlie Brown. Peppermint Patty frequently plays "lovers' games" with Charlie Brown, and gets frustrated or even angry when he doesn't take the bait. Originally, Peppermint Patty played reverse psychology; she would often say, "You kind of like me, don't you, Chuck?" when it was clear that it was Peppermint Patty who had the crush on Charlie Brown, while Charlie not only didn't have a crush on her, he also didn't quite know what to make of her. His true love was the unattainable Little Red-Haired Girl, and having a girl actually like him was unexplored territory. Patty frequently denied having a crush on Charlie Brown at first, writing him off as too "wishy-washy." She has also often dismissed Charlie as not being worth it because "I could strike him out on three straight pitches!" Yet it was still obvious to Marcie - and likely to many readers of the strip as well - that Peppermint Patty liked Charlie Brown as more than a friend, "wishy-washy" or not.
In one Sunday strip from 1979 (drawn as part of a storyline in which Charlie Brown was in the hospital), Peppermint Patty essentially admitted to kind of liking Charlie Brown and, in the same strip, Marcie admitted loving "Charles," so far as to affirming her willingness to marry Charlie Brown. Even this strip ended in a denial of sorts - Patty brought Marcie up to the front desk of the hospital and tried to have her admitted as a patient, saying, "I think she's sicker than
is!"
Peppermint Patty often tries to talk to Charlie Brown about matters of the heart (often depicted with both characters sitting under a tree) and even calls him often on the phone (usually taking up the majority of the conversation), but Charlie Brown usually manages to somehow evade the issue, often by simply playing dumb. Patty often grumbles, "I hate talking to you, Chuck!" whenever she tries to confide in him and he doesn't tell her what she wants to hear.
Peppermint Patty also developed a crush on Pig-Pen for a while in 1980, after Charlie Brown set them up on a date for a Valentine's Day dance. Also, in the movie Bon Voyage, Charlie Brown, both she and Marcie were shown as being attracted to Pierre, the son of their host family in France. Pierre only returned Marcie's affections, however, a fact to which Peppermint Patty remained oblivious even when they were holding hands right in front of her.
http://en.wikipedia.org/wiki/Peppermint_Patty#Relationships_with_other_characters