"She's not my girlfriend!" Except... she totally is, Robin.
"Yes, Star literally forced Robin to compliment her in 'Stranded'."
"She also led him on about the 'girlfriend' thing. She gave him the impression that she thought he was denying they were friends. But she clearly tells him, after he tries to explain, that she KNOWS what 'girlfriend' means. She was therefore actually trying to TRICK him into admitting that she was his girlfriend. And no, this time I don't think she was just being an airhead again; hermanners and behaviour toward him in that ep CLEARLY show that she was being manipulative, not naive."
...Right.
Because it's not like Robin completely led her on or gave her any justifiable reason to think she already was his girlfriend (in her vague understanding of the word at least), you know, at all.
What with...
...taking her on Ferris wheel rides, alone, to watch fireworks and eat cotton candy with him...
...going on an honest-to-goodness date with her, ON VALENTINE'S DAY, during which he...
...holds her hand...
...takes her to the carnival again and tries to win her a prize...
...consents to go on a Tunnel of Love boat ride with her...
...and reassures her he's glad to be spending time with her.
(And this issue makes absolutely no sense continuity-wise given its events and characterization unless it occurs sometime during Season One.)
Not to mention...
...inviting her to dance with him at Prom, just after he and she have been crowned King and Queen...
...becoming noticeably jealous and over-focused on the fact that she's getting married...
...and telling he's glad she isn't getting married...
...constantly
CONSTANTLY
spending time with her...
...and giving her affectionate physical touches.
Which he also lets her give to him.
Yeah. That's totally not sending her the signal that he likes likes her at all.
/sarcasm.
No seriously. According to Starfire's own definition of "girlfriend", she and Robin pretty much filled all the criteria.
1. She is a female.
2. Who has a pleasant and special association with him.
3. Which includes the sharing of enjoyable recreation.
About the only thing we hadn't seen the boy do was buy her flowers. Given everything else however, it's no surprise she assumed she was Robin's girlfriend, based on her rudimentary and mostly technical understanding of the word. Robin really should have seen it coming. For real. You took her on a date you dork, how is she not supposed to think she's your girlfriend? No wonder she was confused in "Stranded".
But of course, since Robin fails at understanding emotions and feelings and girls in general like the socially awkward geek he is, he didn't realize that his romantic affections towards her were, in fact, totally leading her on and making her think he most definitely liked her in the Boyfriend/Girlfriend way. Which he did, but he was too emotionally stunted to admit it. Hence, "Stranded", wherein they clear up their misunderstanding and he realizes, "Yeah, I think I kind of DO like her Like That."
Once again, my rival shippers baffle me in how grossly and willfully they misread the text.
Occam's Razor people. The simplest explanation (that Starfire knew vaguely what being a girlfriend entailed but may not have fully understood the romantic connotations necessary), is usually the right one.