Amanda Bynes Barricades Herself In Dressing Room for 2-Hours

Amanda Bynes went shopping today in West Hollywood ... and locked herself in a dressing room for nearly 2 hours.

Amanda was shopping at Kin (above) -- a hip boutique. Amanda took some clothes inside the fitting room and stayed for 1 hr. 45 min.

The clerks heard a banging sound coming from inside the dressing room every 10 minutes or so. One clerk made a distress call to another employee, saying he was concerned about Bynes being hold up for so long. The employee drove to the store to help, to no avail. Amanda wouldn't come out, telling them, "I need more time."

Amanda finally came out at around 5:30 PM, went to the register and bought a pair of stilettos, a pair of sunglasses and a few other things.

Now get this ... as Amanda walked out she noticed she had tried on a bathing suit top that was underneath her dress and told the clerk she forgot it was on. Amanda then paid for the suit.

Amanda saw a few photogs before leaving and then asked the clerk to call her a cab. It's unclear how she arrived at the store.