In Kesubos 2b there is a discussion in which an answer is introduced with the phrase פשיט רב אחאי – R. Achai answered.
There is a discussion in Tosafos as to the identity of R. Achai. Rashbam claims that this is R. Achai Gaon, the author of the Sheiltos, and because he lived after all the amoraim he always has a different word associated with him such as פריך רב אחאי or פשיט רב אחאי.
Rabbeinu Tam rejects the view of Rashbam, and offers a different reason for the unique words associated with R. Achai. He asserts that every amora had their own unique words so the fact that R. Achai also had unique words does not indicate that he was not a regular amora. Rabbeinu Tam provides three examples of words unique to specific amoraim 1) מגדף בה ר' אבהו (3 תהי בה ר' יוחנן (2 לייט עלה אביי.
The question is: is all this talk about unique words actually true?
There are in fact 9 places in the Talmud where a point is introduced with פריך and in all 9 cases the person doing the פריך is R. Achai/Acha. (Yevamos 24a, Yevamos 46a, Kesubos 47a, Kiddushin 13a, Shavuos 41b, Zevachim 102b, Chullin 65b, Bechoros 6a, Niddah 33a.)
However, פשיט is only used once in reference to R. Achai (our case under discussion), while it is used on several occasions for other amoraim (though granted not in the precise format of פשיט רב פלוני).
While תהי בה is indeed used for R. Yochanan more often than for other amoraim (Kesubos 107b, Kiddushin 55b, Bava Kamma 112b, Bava Basra 39a, Bechoros 42b,) it is still used for a whole bunch of amoraim, such as R. Zera (Berachos 38b), Reish Lakish (Zevachim 13b), R. Elazar (Eruvin 66a, Bava Kamma 76b), such that it is a bit of a stretch to call it R. Yochanan's unique lashon. In fact, in the parallel passage in Tosafos HaRosh one of the examples given of unique words is תהי בה ר' זירא!
Similarly, the term מגדף בה is used most often for R. Abahu (Shabbos 62b, Sanhedrin 3b, Sanhedrin 40b, Zevachim 12a) but it is also used for R. Yirmiyah (Avodah Zarah 35a) and R. Chanina (Avodah Zarah 43a).
Similarly, the term לייט עלה is used primarily for Abbaye (Berachos 29a, Shabbos 120b, Pesachim 104a, Taanis 29b, Moed Katan 12b, Kiddushin 33b) but it is also used for Rav (Shabbos 120b). If we include other variations (such as לייט אמאן) we can include several others as well (e.g. R. Yehoshua Ben Levi, R. Chisda).
While it is possible that Rabbeinu Tam meant not that these words were unique to these amoraim, but that these amoraim always used these words, it would still be a stretch because each of these amoraim only use their specific words a few times in the entire Talmud (aside from פריך רב אחאי/אחא which is used 9 times).
Furthermore, the phrasing employed by Rabbeinu Tam וכל אמורא היה תופס לשונו implies that each amora chose his unique word. However, the unique words in question are all verbs describing actions taken by the amoraim. Therefore the amoraim were not using these words themselves; rather, the redactors of the Talmud chose to use certain words to describe the actions of certain amoraim.
If we grant that it was the redactors that chose the unique words we have another problem: if, in accordance with the theory of Rabbeinu Tam, these unique words were used deliberately for specific amoraim, why did the redactors sabotage their goal by also using the same words for other amoraim once in a while?
(I have not found any subsequent sources that deal with this issue.)