Gallagher, 41, was seen at The Holly Bush in Hampstead, north London, shortly before last call during a recent night out, UK newspaper the Sunday People reports.
The paper said Gallagher looked dishevelled and was "behaving strangely" before he got into an argument with the bartender over his tab.
"He was making a real nuisance of himself even before he got kicked out," a source said.
"He was acting irrationally and started kicking off and swearing after the barman told him he hadn't paid for his drinks. He took exception to what the barman had said and started giving it the big ... 'I'm famous!'"
Gallagher was reportedly seen heading to the bathroom with a bouncer suspecting the rocker of doing drugs and banning him from the bar.
"He accused him of snorting cocaine off the toilet seat and said there was still some left on the seat even after he came out," the insider said.
"Apparently Liam hadn't even bothered locking the door. Liam wasn't happy about being thrown out.
"The bouncer told him 'you're barred' and he was like 'Are you joking?' It was embarrassing to watch."
A representative for Gallagher declined to comment.
The Holly Bush, a known celebrity haunt in walking distance from Gallagher's home, also declined to comment.
As The Mirror reports, Gallagher has faced legal troubles in the past due to drugs-related issues.
In 1996, the rocker accepted a police caution for cocaine possession.
In 2009, however, Gallagher said he had not taken the drug for nearly a year and was determined to remain clean for his children.
Gallagher shares a 16-year-old daughter with singer Lisa Moorish and sons, age 12 and 14, with actress Patsy Kensit. He also has a 15-month-old daughter with journalist Liza Ghorbani.
