Green’s Dictionary of Slang

1. to speak in any form of extreme manner – flattery, telling a ‘hard-luck story’ – in order to gain money or emotional advantage.

1934		W.R. Burnett Goodbye to the Past 201: He had promised Bill there would be no talk of business, but the Judge was pouring it on, hardly giving Bill a chance to say a word.
1942		W.R. Burnett Quick Brown Fox 230: He wanted, he said, to draw the suckers in first, get them interested, and then later pour it [i.e. the hard sell] to them.
1956		J. Stearn Sisters of the Night 68: That Patsy sure knew how to pour it on. All evening she cried.
1986		R. Campbell In La-La Land We Trust (1999) 148: You shake your head in shocked dismay. You cluck your tongue. You twist and turn and pour it on.

2. (orig. US) to make a great effort; to intensify one’s efforts; of a vehicle, to accelerate.

1939		Howsley Argot: Dict. of Und. Sl.
1953		J. Thompson Savage Night (1991) 25: ‘Stop what?’ I said, pouring it on all the harder.
2001		‘Randy Everhard’ Tattoo of a Naked Lady 97: I poured it on, dusting the pigfucker. Soon his headlights were only pinpoints in the rearview.

3. (also pour it to) to punish harshly.

1953		T. Runyon In For Life 151: They weren’t even pouring it on me for the crime I was charged with.
1961		M. Braly Felony Tank (1962) 86: They won’t be too harsh on you your first time. But if you’re mixed up in this, they’ll pour it to you.

4. (US) to seek a verbal or physical confrontation.

1968

‘Hy Lit’ Hy Lit’s Unbelievable Dict. of Hip Words 10: come on strong – Pouring or laying it on; getting tuff; starting trouble; being fresh; showboating; looking for trouble.

5. to have sexual intercourse.

1964

J. Thompson Pop. 1280 in Four Novels (1983) 393: A woman still might have a dummy pour it on her than a normal fella.