Katy Perry/WMG


 * "I kissed a girl" takes on more meaning when you realize it came out after "UR so gay", where Katy was mocking her "gay" boyfriend. Now, imagine she and this guy stayed/got back together. Then the events of "I kissed a girl" take place. Katy kisses a girl (and she LIKES IT!). "I hope my boyfriend don't mind it"? More like if he finds out you'll learn just what a fierce bitch payback can be, Katy. It's also possible Katy was being such a jerk about her boyfriend's "gayness" due to her homophobia, which is rooted in subconscious anxiety over her own feelings of same-sex attraction. And yes, I do think the boyfriend in question could very well be Russell Brand.

Katy Perry is an Attention Whore
Which would explain EVERYTHING.

'I Kissed A Girl' is about a lesbian (or bisexual girl) in denial.
The random mention of her boyfriend and the insistent justification that she's not REALLY interested that way and the kissing is innocent while fawning over how magical girls are reek of this. Also, the motivation of why she'd deny it so fiercely is there too, she feels guilty ('It felt so wrong, it felt so right.') due to social conditioning since 'it's not what good girls do'.
 * Also, her boyfriend probably wouldn't mind her kissing a girl - unless he knew she was actually attracted to girls.

Katy Perry is an alien
And she's from a planet that has been locked in a centuries-long conflict with whatever planet Lady Gaga came from. They were both sent as emissaries to Earth to try and compete for the hearts and minds of humanity.
 * Hm, maybe her song 'E.T.' is about an earthling, then? Technically alien to her.
 * Yup. She came to Earth and expected to have a lot of interaction with us humans as her planet competed against Lady Gaga's planet for the Earth's allegiance...she just never expected that she was going to fall in love with one of us Earthlings (Russell Brand). So the song is about her dealing with her confusion over this inter-species romance....what she doesn't realize is that Russell Brand himself is also an alien from a third planet.

Katy Perry is a Magical Girl from an anime who has broken the fourth wall
...and entered our world. This explains the colorful wardrobe, the unusually large eyes, the color hair, and her Blithe Spirit persona. She's a Genki Girl, Magical Girl, and a Manic Pixie Dream Girl, and she just wants to have fun. She's slowly trying get all of humanity of embrace this mindset...and when we do, the whole world will become one big beach party. And it will be awesome.