I've been really enjoying "The Zoological Gardens" recently. Great tune. Funny lyrics, both kinds of entendre, both single and double. Sung by Brendan Behan and also by the Dubliners (the Dubliners version is great). Have a listen on Spotify. You can use the "Trouble and strife, it is no lark..." verse as a chorus, as Behan does.

There's always 'The Black Velvet Band'. A terrible old chestnut, I know, but it definitely has the singalongability factor in the chorus.

"A Pub With No Beer", another Dubliners song you can hear on Spotify, is a pretty obvious pub singalong that's pretty foolproof.