Don't mess with Ribbi Yohanan

בבא קמא קיז.
ההוא גברא דהוה בעי אחוויי אתיבנא דחבריה אתא לקמיה דרב א"ל לא תחוי ולא תחוי א"ל מחוינא ומחוינא יתיב רב כהנא קמיה דרב שמטיה לקועיה מיניה קרי רב עילויה (ישעיהו נא) בניך עולפו שכבו בראש כל חוצות כתוא מכמר מה תוא זה כיון שנפל במכמר אין מרחמין עליו אף ממון של ישראל כיון שנפל ביד <עובדי כוכבים> {גוים} אין מרחמין עליו א"ל רב כהנא עד האידנא הוו פרסאי דלא קפדי אשפיכות דמים והשתא איכא [רומאי] דקפדו אשפיכות דמים ואמרי מרדין מרדין קום סק לארעא דישראל וקביל עלך דלא תקשי לרבי יוחנן שבע שנין אזיל אשכחיה לריש לקיש דיתיב וקא מסיים מתיבתא דיומא לרבנן אמר להו ריש לקיש היכא אמרו ליה אמאי אמר להו האי קושיא והאי קושיא והאי פירוקא והאי פירוקא אמרו ליה לריש לקיש אזל ריש לקיש א"ל לרבי יוחנן ארי עלה מבבל לעיין מר במתיבתא דלמחר למחר אותבוה בדרא קמא קמיה דר' יוחנן אמר שמעתתא ולא אקשי שמעתתא ולא אקשי אנחתיה אחורי שבע דרי עד דאותביה בדרא בתרא א"ל רבי יוחנן לר"ש בן לקיש ארי שאמרת נעשה שועל אמר יהא רעוא דהני שבע דרי להוו חילוף שבע שנין דאמר לי רב קם אכרעיה א"ל נהדר מר ברישא אמר שמעתתא ואקשי אוקמיה בדרא קמא אמר שמעתתא ואקשי ר' יוחנן הוה יתיב אשבע בסתרקי שלפי ליה חדא בסתרקא מתותיה אמר שמעתתא ואקשי ליה עד דשלפי ליה כולהו בסתרקי מתותיה עד דיתיב על ארעא רבי יוחנן גברא סבא הוה ומסרחי גביניה אמר להו דלו לי עיני ואחזייה דלו ליה במכחלתא דכספא חזא דפרטיה שפוותיה סבר אחוך קמחייך ביה חלש דעתיה ונח נפשיה למחר אמר להו רבי יוחנן לרבנן חזיתו לבבלאה היכי עביד אמרו ליה דרכיה הכי על לגבי מערתא חזא דהוה
 הדרא ליה עכנא א"ל עכנא עכנא פתח פומיך ויכנס הרב אצל תלמיד ולא פתח יכנס חבר אצל חבר ולא פתח יכנס תלמיד אצל הרב פתח ליה בעא רחמי ואוקמיה א"ל אי הוה ידענא דדרכיה דמר הכי לא חלשא דעתי השתא ליתי מר בהדן א"ל אי מצית למיבעי רחמי דתו לא שכיבנא אזילנא ואי לא לא אזילנא הואיל וחליף שעתא חליף תייריה אוקמיה שייליה כל ספיקא דהוה ליה ופשטינהו ניהליה היינו דאמר ר' יוחנן דילכון אמרי דילהון היא:

Bava Kama 117a (Soncino Press translation)
A certain man who was desirous of showing another man's straw [to be confiscated] appeared before Rab, who said to him: 'Don't show it! Don't show it!' He retorted: 'I will show it! I will show it!' R. Kahana was then sitting before Rab, and he tore [that man's] windpipe out of him [in a martial-arts-like manner]. Rab thereupon quoted: Thy sons have fainted, they lie at the heads of all the streets as a wild bull in a net;  just as when a 'wild bull' falls into a 'net' no one has mercy upon it, so with the property of an Israelite, as soon as it falls into the hands of heathen oppressors no mercy is exercised towards it.35  Rab therefore said to him: 'Kahana, until now the [Persians]  who did not take much notice of bloodshed were [here and had sway, but] now the [Romans]  who are particular regarding bloodshed are here, and they will certainly say, "Murder, murder!";  arise therefore and go up to the Land of Israel but take it upon yourself that you will not point out any difficulty to R. Johanan  for the next seven years. When he arrived there he found Resh Lakish sitting and going over  the lecture of the day for [the younger of] the Rabbis.  He thereupon said to them: 'Where is Resh Lakish?'  They said to him: 'Why do you ask?' He replied: 'This point [in the lecture] is difficult and that point is difficult, but this could be given as an answer and that could be given as an answer.' When they mentioned this to Resh Lakish, Resh Lakish went and said to R. Johanan: 'A lion  has come up from Babylon; let the Master therefore look very carefully into tomorrow's lecture.' On the morrow R. Kahana was seated on the first row of disciples before R. Johanan, but as the latter made one statement and the former did not raise any difficulty, another statement, and the former raised no difficulty, R. Kahana was put back through the seven rows until he remained seated upon the very last row. R. Johanan thereupon said to R. Simeon b. Lakish: 'The lion you mentioned turns out to be a [mere] fox.'  R. Kahana thereupon  whispered [in prayer]: 'May it be the will [of Heaven] that these seven rows be in the place of the seven years mentioned by Rab.' He thereupon immediately stood on his feet  and said to R. Johanan: 'Will the Master please start the lecture again from the beginning.' As soon as the latter made a statement [on a matter of law], R. Kahana pointed out a difficulty, and so also when R. Johanan subsequently made further statements, for which he was placed again on the first row. R. Johanan was sitting upon seven cushions. Whenever he made a statement against which a difficulty was pointed out, one cushion was pulled out from under him, [and so it went on until] all the cushions were pulled out from under him and he remained seated upon the ground. As R. Johanan was then a very old man and his eyelashes were overhanging he said to them, 'Lift up my eyes for me as I want to see him.' So they lifted up his eye[lashes] with silver pincers. He saw that R. Kahana's lips were parted  and thought that he was laughing at him. He felt aggrieved and in consequence the soul of R. Kahana went to rest.  On the next day R. Johanan said to our Rabbis, 'Have you noticed how the Babylonian was making [a laughing-stock of us]?' But they said to him, 'This was his natural appearance.' [Rav Kahana was not laughing at Ribbi Yohanan, he was simply funny-looking.] He thereupon went to the cave [of R. Kahana's grave] and saw a snake coiled round it. He said: 'Snake, snake, open thy mouth  and let the Master go in to the disciple.' But the snake did not open its mouth. He then said: 'Let the colleague go in to [his] associate!' But it still did not open [its mouth, until he said,] 'Let the disciple enter to his Master,' when the snake did open its mouth.  He then prayed for mercy and raised him.  He said to him, 'Had I known that the natural appearance of the Master was like that, I should never have taken offence; now, therefore let the Master go with us.' He replied, 'If you are able to pray for mercy that I should never die again [through causing you any annoyance],  I will go with you, but if not I am not prepared to go with you. For later on you might change again.' R. Johanan thereupon completely awakened and restored him and he used to consult him on doubtful points, R. Kahana solving them for him. This is implied in the statement made by R. Johanan: 'What  I had believed to be yours  was In fact theirs.

A"A compared this gemara to the story of the death of Rish Lakish (recorded in Bava Metsia, 84a), also at the hands of Ribbi Yohanan's hak'pada. Don't mess with Ribbi Yohanan.