Sorry I can only understand little Japanese. I guess the word you are looking for is "pet phrase" or "tag", "pet phrase" is more casual. Hope it's helpful to you

.Probably "favorite phrase".

When I first read this, I was like, " What the heck is 口癖 ? I'm a native speaker of Chinese and this one is really beyond me." It turns out this is not Chinese but Japanese. The closest thing I can get is "habitual words". To help you get the best possible answer, I am taking the liberty of explaining this Japanese to those who cannot read Japanese kanji: The Japanese phrase 口癖 (kuchiguse) means the words one repeatedly use in sentences. Those words very often mean very little, and the speaker are very often oblivious to the fact that they are over using them. Some of the examples of these habitual words in English could be "you know", "like", "anyway", etc. However, one aspect of kuchiguse in Japanese that distinguishes it from the examples given above is that it is equally common for kuchiguse to appear as some kind of suffix or participle, or a thingy attached to existing words. The y at the end of thingy is actually a good example here.