These are ambient dialogue lines heard when standing near Clem, either in Darvo's shop, Cressa's Garrison, or Iron Wake.
Clem's name is derived from the word "klem" [them], commonly spoken by Grineer troops in a variety of sentences (eg "Get klem!" [Get them!]). The character was developed by Datareaper on tumblr, and gained popularity within the community. Eventually the development team noticed and incorporated Clem within the game. Many of Clem's irregular traits stem from the original comics by Datareaper.
After Clem is introduced in A Man of Few Words, he will stand next to Darvo in his shop on the Relays. He will also infrequently take the place of the medallion vendor in Cressa's Garrison, the Steel Meridian enclave on the Relays. After the Chains of Harrow quest, he can also be found in a "blunt-fort" in a deserted corner of Iron Wake, where he is eventually joined by a Ghoul defector and Popcorn, the Jackal test Moa. Clem is mentioned by Cephalon Cordylon and by Domineering Sisters of Parvos, and is referenced in a possible Steel Meridian crewmember's bio.