Girls how come PDA don't bother you?

ok i'm not saying all girls but most girls i've been with has no problem with making out in public, my girl friend hates when some one burp loud in public she's like a perfectionist want every thing to be neat clean and perfect. but still she has no problem making out in public in the mall she'll be grabbing and touching me and kissing me even at her work (she's a bar tender) now it bothers me a lot, i think pda is very rude but i have no problem burping just that. so who's dowing the wrong thing here?