The Republican party is a very divided group based on the events of the most recent election. The group members have attacked each other consistently throughout the campaign season, so it is no surprise that Mitch McConnell was not received well at the convention. It is appropriate that his opponents provided a negative reaction to his appearance on the stage, as it is their right to express their dissatisfaction with his actions.
Republican leadership has been promising their base over the top goals for years. After all this time and the reassurances, the party has chosen someone they think can deliver those promises, and will do so as clear repudiation of the ineffectual leadership. The chickens have come home to roost, which is why those chickens were right to boo.
Senate Majority Leader (Rep) Mitch McConnell received the jeering of the RNC. If anyone is surprised by this, they only need to look at his track record over the past year. From consistent refusals to compromise to the audacity to claim that the president is unable to name a Supreme Court Judge during his final year in office, McConnell has consistently proven what is wrong with the Republican party and what separates them from the party that they once were.
Even though they may have disagreed with his ideas that does not mean it appropriate to boo him. Booing is very disrespectful, and the booing of Mitch McConnell is a perfect example of how far out of line certain factions of the Republican Party have gone. It is a bad sign.